Aquatic Invasions (2016) Volume 11 Issue 3 257ndash266 DOI httpdxdoiorg103391ai201611304

copy 2016 The Author(s) Journal compilation copy 2016 REABIC

Open Access

257

Research Article

An invasive polychaete species found in living marine stromatolites

Nelson AF Miranda1 Elena K Kupriyanova2 Gavin M Rishworth1 Nasreen Peer1 Thomas G Bornman34 Matthew S Bird1 and Renzo Perissinotto1 1DSTNRF Research Chair in Shallow Water Ecosystems Nelson Mandela Metropolitan University Port Elizabeth 6031 South Africa 2Australian Museum Research Institute Australian Museum 1 William Street Sydney NSW 2010 Australia 3South African Environmental Observation Network Elwandle Coastal Node Port Elizabeth South Africa 4Coastal and Marine Research Institute Department of Botany Nelson Mandela Metropolitan University Port Elizabeth South Africa

Corresponding author

E-mail mirandanafgmailcom

Received 15 January 2016 Accepted 28 April 2016 Published online 14 May 2016

Handling editor Elisabeth Cook

Abstract

This study represents the first report of an invasive species associated with modern living stromatolites The presence and potential impacts of the reef-forming tubeworm Ficopomatus enigmaticus (Fauvel 1923) in unique stromatolite ecosystems of South Africa are addressed Data on F enigmaticus populations and a suite of environmental variables were collected on a monthly basis in 2014 at three sites along the Eastern Cape coast Results are interpreted in terms of known environmental tolerance reproductive strategy and environmental impacts of F enigmaticus around the world A combination of variables influenced the F enigmaticus populations particularly temperature and the availability of substrates for settlement Low water temperatures (lt 20degC) in winter appeared to limit the species growth and reproduction Small populations of adult individuals were however able to persist all year round in habitats that exhibit favourable environmental conditions These stromatolite pools appear to function as unique ecosystems that provide refuge for estuarine species thus acting as stepping stones facilitating the dispersal and range expansion of estuarine fauna along the coast including invasive species

Key words tubeworm settlement temperature tolerance stepping stones refuge range expansion

Introduction

During the last two decades marine invasive species have been reported from virtually every coastal ecosystem worldwide (Ruiz et al 1997 Bax et al 2003 Gallardo et al 2016) A number of drivers act either singularly or synergistically (Lau and Schultheis 2015) to prompt an invasion Such drivers include disturbance propagule pressure human-mediated transport low biotic and abiotic resistance and shifting climate regimes (Blackburn et al 2015 Bellard et al 2016 Penk et al 2016) Refugia or stepping-stones can affect spread by allowing organisms to utilise smaller sometimes unfavourable (Apte et al 2000) habitats to expand their distribution from and to preferred environments

The recent discovery of an extensive network of peritidal stromatolite pools along the South African coastline (Smith et al 2005 Smith et al 2011

Perissinotto et al 2014) is therefore of interest because they appear to provide refugia and may function as stepping stones for invasive species Stromatolites (layered microbialites) are formed through the deposition of calcium carbonate and the trapping of sediment by microalgae predominantly cyanobacteria and diatoms (Reid et al 2000 Bosak et al 2013) Marine living stromatolites are rare and considered to be partial analogues (Riding 2011) of those ancient microbialites that dominated shallow Archean and Proterozoic oceans (Grotzinger and Knoll 1999 Riding 2011) The stromatolites discovered in South Africa are similar in structure but less extensive and marine-influenced compared to those found in south-western Australia (Forbes et al 2010) and Northern Ireland (Cooper et al 2013) They are formed at the intersection of fresh carbonate-rich groundwater discharge and the upper subtidal marine zone (Perissinotto et al 2014)

NAF Miranda et al

258

Figure 1 Map of the study area showing the sampling locations on the south coast of South Africa (A B and C) as well as the location of all coastal freshwater seeps in the surrounding area from Cape Recife to Oyster Bay (black dots 540 in total) Two stromatolite pools uninvaded by F enigmaticus were sampled at site A three invaded pools were sampled at site B one invaded and two uninvaded pools were sampled at site C Adapted from Perissinotto et al (2014)

South African stromatolites host a wide variety of freshwater estuarine and marine organisms that appear to alternate their dominance in response to vertical mixing and the balance between freshwater and seawater inputs (Perissinotto et al 2014) Among these species is the invasive estuarine tubeworm Ficopomatus enigmaticus (Fauvel 1923) The species is suspected to originate from temperate regions of the Indian Ocean but geographic origin is still uncertain and a matter of debate (reviewed by Dittmann et al 2009) The species was first recorded in South Africa (as Mercierella enigmatica) in the 1950rsquos (Day 1951) and is thought to have been introduced by ship fouling from southern or western Australia (Mead et al 2011a) Presently most estuaries in South Africa are colonised by this alien species (Day 1981 Plisko and Griffiths 2011) and it is suspected that stromatolite pools act as stepping-stones in the spread of this species across estuarine systems that are often located far apart from each other This serpulid tubeworm is considered to be a highly invasive ecosystem engineer that has colonised many subtropical and temperate areas of the world (ten Hove and Weerdenburg 1978 Day 1981 Fornos et al 1997 Bianchi and Morri 2001 Mead et al 2011b Pernet et al 2016) It builds large reefs on hard

substrates including artificial structures and has had major impacts on the ecology of systems it invaded in Argentina and South Africa (Obenat and Pezzani 1994 Schwindt and Iribarne 2000 Bianchi and Morri 2001 Schwindt et al 2001 Schwindt et al 2004a Schwindt et al 2004b Dittmann et al 2009 McQuaid and Griffiths 2014)

This study represents the first report of an invasive species associated with living stromatolites Modern stromatolites along the South African coast are characterised by highly variable environmental conditions with frequent and extreme fluctuations associated with regular spring tidal over-topping and flushing with freshwater from groundwater (Perissinotto et al 2014) This high variability creates a unique habitat suited only to those species able to tolerate extreme environmental fluctuations Our goal was to examine the presence and potential impacts of the reef-forming tubeworm F enigmaticus in stromatolite ecosystems This was done by assessing population abundance patterns and growth rates of the tubeworm in stromatolite pools to determine the most important environmental variables correlated to tubeworm populations by comparing invaded and uninvaded habitats in terms of environmental variables

Invasive polychaete in marine stromatolites

259

Table 1 Stromatolite pools sampled on the south coast of South Africa Eight pools were surveyed in total four invaded and four uninvaded by Ficopomatus enigmaticus

Pools Pool number Site Status

Three upper pools (sensu Perissinotto et al 2014) contained stromatolite structures and were located nearest to freshwater seepage points

1 A Uninvaded by F enigmaticus

2 B Invaded by F enigmaticus

3 C Uninvaded by F enigmaticus

Three middle pools contained the most stromatolite accretion and are considered typical barrage pools (Perissinotto et al 2014) They were located between seepage points and the subtidal zone

4 A Uninvaded by F enigmaticus

5 B Invaded by F enigmaticus

6 C Uninvaded by F enigmaticus

Two additional pools were situated nearer to seepage points than the subtidal zone These contained stromatolite structures and relatively high numbers of live F enigmaticus as well as empty tubes attached to boulders

7 B Invaded by F enigmaticus

8 C Invaded by F enigmaticus

Methods

Study sites and sample collection

Samples were collected in 2014 during the first extensive survey of the three barrage pool sites reported by Perissinotto et al (2014) Collection sites were located west of Cape Recife (site A 34ordm02prime4213PrimeS 25ordm34prime0750PrimeE) at Schoenmakerskop (site B 34ordm02prime 2823PrimeS 25ordm32prime1860PrimeE) and east of Seaview (site C 34ordm01prime0316PrimeS 25ordm21prime5648PrimeE) along the South African coastline in the vicinity of Port Elizabeth (Figure 1) Sampling was conducted at lowest low-tide during the first spring tidal phase of each month during each season (autumn Mar ndash May winter Jun ndash Aug spring Sep ndash Nov summer Dec ndash Feb)

The current study focused on middle and upper pools in sites A B and C (see Perissinotto et al 2014) as well as two additional pools one at site B and one at site C (Figure 1 Table 1) All pools in this study were located between the subtidal waterline and landward groundwater seepage Lower pools (sensu Perissinotto et al 2014) were closest to the subtidal had the least stromatolite growth and always contained marine organisms with no trace of F enigmaticus Therefore lower pools were not included in this study

A YSI 6600-V2 multiprobe system (YSI Incorporated Yellow Springs Ohio USA) was used to measure physico-chemical parameters in all pools temperature (degC) salinity depth (m) pH turbidity (NTU) and dissolved oxygen (DO mgl-1) Star Oddi DST CT (httpwwwstar-oddicom) probes were deployed in crevices at the bottom of each middle pool and

recorded hourly temperature and salinity data Additional information that influences all pools was also collected for the study area Rainfall as measured by the South African Weather Services at the Port Elizabeth International Airport (~ 9 km from Site B) influences freshwater input to all the pools Swell height as modelled by Windguru (httpwwwwindgurucz) for Port Elizabeth was considered an indicator of environmental energy as the pools are regularly over-topped by saltwater during spring high tides and storm surges Inshore ocean surface temperature was measured using Onset Hoboreg U22-001 underwater temperature recorders (Onset Cape Cod Massa-chusetts USA) deployed at depths lt 1 m below mean spring low water Ficopomatus enigmaticus are suspension feeders known to filter large volumes of water (Davies et al 1989) hence potentially affecting total suspended solids (TSS) particulate organic matter (POM) and chlorophyll-a (chl-a) concentra-tions Water samples were collected monthly from pools to determine TSS (mgl-1) POM (mgl-1) and chl-a (mgm-3) Water was filtered through pre-combusted and pre-weighed Whatman GFF filters Filters with retained materials were oven dried (60degC for 48 h) and weighed with a digital balance (001 mg) to determine TSS (total dry mass) and then combus-ted (450degC for 4 h) and weighed again to determine POM (organic component) For water-column chl-a analyses water was filtered through a GFF filter To extract pigments filters with retained material were placed in 8 ml of 90 acetone solution for 48 h in darkness at 4degC Fluorescence was measured using a Turner 10-AU narrow-band system (Turner Designs Sunnyvale California USA)

NAF Miranda et al

260

The availability of substrates suitable for colonisation by F enigmaticus was estimated every month Objects larger than 500 cm3 (such as bottles cans tree trunks and other debris) were regarded as substrates on which F enigmaticus could settle (Schwindt and Iribarne 2000 Schwindt et al 2004a) and were counted in each pool Algal mats can cover hard substrates and effectively create a physical barrier to larval settlement (Norkko and Bonsdorff 1996) Therefore to calculate the total (algae-free) area potentially available for the settlement of F enigmaticus during this study the total hard substrate area of each pool was measured and the percentage benthic algal cover was estimated based on photo-quadrats A 12 megapixel digital camera was positioned 15 m over a 1 times 1 m PVC quadrat which was placed on the water surface and aligned according to landmarks The entire water surface of pools was photographed every month in this way

All pools were searched for traces of tubeworms every month The number of live F enigmaticus individuals was counted in each pool and the length of their calcareous tubes was measured with Vernier callipers (to the nearest 001 mm) Tube growth (increase in length mm) was also tracked for each live individual worm found Photographs were used to confirm the identity of individuals as each displayed distinct settlement locations and tube shapes Measurements were repeated every 30 days and used to determine tube length increases of individual worms Average monthly tube growth rate (increase in length) was then calculated for invaded pools To determine dry mass (biomass) worms (5 individuals per pool) were separated from their tubes oven dried (60degC for 48 h) and individually weighed to the nearest 001 mg

Statistical analyses

General linear models (GLM) with quasi-Poisson distribution (season four levels autumn winter spring summer status two levels invaded and uninvaded) were run for each environmental variable (TSS POM chl-a temperature salinity depth pH turbidity dissolved oxygen potential available area for settlement potential substrates for settlement) followed by Tukeyrsquos post-hoc testing to determine if there were significant differences between invaded and uninvaded pools in each season ANOVA followed by Tukeyrsquos post-hoc test was used to determine if there were differences between seasons in log(x+1) transformed F enigmaticus tube growth data In both cases all model assumptions were met These analyses were done using the statistical software R version 2151

Figure 2 Ficopomatus enigmaticus tubeworms on colloform formations in a stromatolite pool along the south coast of South Africa (a) ventral view (b) dorsal view (c) and operculum (d) of extracted specimen Photographs by NAF Miranda

Non-parametric permutational MANOVA (PERMANOVA Anderson et al 2008) was used to test for differences in the measured environmental variables In this regard a three-way PERMANOVA design tested for differences between pools uninvaded and invaded (UI) by F enigmaticus (fixed term 2 levels) pools (random factor nested in UI 8 levels) and seasons (fixed factor four levels) The resemblance matrix was based on Euclidean distance Statistical significance was tested using 9999 permutations of residuals under a reduced model Distance-based linear modelling (DISTLM Legendre and Anderson 1999 McArdle and Anderson 2001 Anderson et al 2008) was used to perform permuta-tional regression (9999 random permutations) to test for linear relationships between F enigmaticus abundance (response) and the above-mentioned environmental variables (predictors) The response variable (F enigmaticus abundance) was first converted to a Euclidean distance matrix A step-wise selection procedure was used incorporating the corrected Akaike Information Criterion (AICc) (Burnham and Anderson 2002) as the selection criterion to measure the relative goodness of fit for each model The final subset of environmental variables that provided maximum parsimony (according to the AICc criterion) is presented The a priori significance level (α) for all multivariate tests was set at 001

Invasive polychaete in marine stromatolites

261

Figure 3 Rainfall ocean temperature and swell height data collected in the study area (a-c) selected environmental variables (water temperature salinity available potential area for settlement and pool depth) collected from four stromatolite pools invaded by F enigmaticus (red solid line) and four uninvaded pools (blue dashed line) (d-g) monthly F enigmaticus tube growth in invaded pools (h) and number of F enigmaticus individuals (abundance) per invaded pool (i) Data were collected in 2014 and are presented as monthly means (plusmn SD)

Results

The highest mean TSS and POM values were recorded during summer (supplementary material Table S1) The lowest mean TSS was recorded during spring The lowest mean POM highest mean turbidity and highest mean chl-a were recorded during autumn Temperature was lowest in winter and highest in summer (Table S1 Figure 3) In general all pools were colder and saltier in autumn and winter and warmer and fresher in spring and summer Mean DO ranged between 8 and 12 mgl-1 and mean pH was approximately 8 in all pools While both invaded and uninvaded pools had areas potentially available for settlement throughout the year (Table S1 Figure 3) these were significantly smaller only in uninvaded pools during winter

The density of F enigmaticus was greatest in spring reaching mean (plusmn SE) values of 146 plusmn 130 indm-2

(Table S1) During summer the average increase in tube length reached 686 mm per 30 days (Figure 3) However there were no significant differences in tube growth between seasons (ANOVA P gt 005) Individuals had an average dry mass of 023 plusmn 004 mg tube length of 2145 plusmn 216 mm and reached a biomass of up to 9435 mg dry mass per invaded pool (or 2359 mg m-2) After a mass-mortality event at the end of January 2014 (coinciding with a red tide in the Algoa Bay area and the lowest DO readings recorded in the study) no live F enigmaticus individuals were recorded in 3 of the invaded pools (site C additional pool site B upper and additional pool) from February to August However a few large individuals (average biomass 075 plusmn 002 mg and tube length 2786 plusmn 047 mm) persisted in a single pool (middle pool site B) during autumn and winter (total dry mass 747 mg or 062 mgm-2)

NAF Miranda et al

262

Table 2 PERMANOVA test for differences in abiotic variables across F enigmaticus invaded and uninvaded stromatolite pools (IU fixed factor) pools (random factor nested in IU) and seasons (fixed factor) The degrees of freedom df sum of squares SS means squared MS pseudo ndash F statistic and probability level based on 9999 random permutations P(perm) are presented Significant factors are in bold (α = 001) Data were collected in Eastern Cape stromatolite pools in 2014

Source df SS MS Pseudo-F P(perm)

IU 1 39382 394 0606 0778

Seasons 3 22744 758 8440 0001

Pools (IU) 6 39007 650 8488 0001

IU times Seasons 3 21214 71 0787 0754

Pools(IU) times Seasons 18 16169 90 1173 0093

Residuals 64 4902 77 0606 0778

Total 95 1330

Table 3 Distance-based linear regression model of F enigmaticus abundance (response) against environmental variables (predictors) measured in Eastern Cape stromatolite pools in 2014 (A) Sequential tests for stepwise model (R2 = 026) and percentage of multivariate variation explained by individual axes are presented (B) The most parsimonious model included number of potential substrates for settlement ldquoSubstratesrdquo stromatolite pool water temperature ldquoTemprdquo and available potential area for settlement ldquoAreardquo

A Model summary

Variable AICc SS (trace) Pseudo - F P Prop Cumul res df

Substrates 62640 78690 1180 lt 001 0111 0111 94

Temp (degC) 62095 47619 764 lt 001 0068 0179 93

Area (m2) 61357 54886 963 lt 001 0078 0257 92 B Variation explained by axes

Axis Individual Cumulative Individual Cumulative

explained variation of fitted model explained variation of total variation

1 9821 9821 2521 2521

2 179 100 046 2567

Mean ocean surface temperature was lowest in spring and highest in summer (January and February) (Figure 3) Mean swell height increased in autumn and peaked in winter with this peak coinciding with an increase in mean salinity recorded in all pools in winter while the highest salinities were recorded in invaded pools (Table S1 Figure 3) There was a clear recruitment event at the onset of spring (AugustSeptember) during which 95 plusmn 49 individuals were recorded per invaded pool (Table S1 Figure 3) This coincided with an increase in mean rainfall (gt 50 mm) and a drop in mean swell height at the end of winter (mean swell height remained at approximately 3 m from August to December)

Significant differences in stromatolite pool abiotic data were detected between seasons and pools (Table 2) No significant differences in abiotic conditions were detected however between invaded and uninvaded pools There were differences among seasons and F enigmaticus presence was greater in spring when temperature TSS and POM were higher in the pools

while swell height was lower and ocean temperature was higher in the study area (Figure 4) The stepwise AICc analysis showed that F enigmaticus abundance exhibited a significant relationship with pool tempera-ture number of substrates and area potentially available for settlement (Table 3) However this three variable model only explained 26 of the total variation in F enigmaticus abundance data

Discussion

Ficopomatus enigmaticus is not an obligate reef builder (Bianchi and Morri 2001) and occurs indivi-dually or in small aggregations in the South African stromatolite pools often attached to rocks directly on stromatolites (Figure 2) or on any other available substrates Availability of settlement substrates and water temperature appear to be the most important variables controlling the persistence of F enigmaticus in stromatolite pools Overall environmental variables explained a low percentage of the variation in F enigmaticus abundance (Table 3) This is expected

Invasive polychaete in marine stromatolites

263

for a habitat generalist with wide environmental tolerance However Schwindt et al (2004a) argued that habitats favoured by F enigmaticus populations are very similar in their physical chemical and biological characteristics throughout the world These authors also suggested that the most important variables that affect the spread of this species in invaded habitats may be salinity nutrients (ie TSS POM and chl-a) and environmental energy (eg current speed or swell height as proxy) The TSS POM and chl-a values measured in the current study correspond with the lowest recorded by Schwindt et al (2004a) and therefore may partially explain the relatively small population size observed in stromatolite pools

The use of estuaries and intermittent water bodies as stepping stones for aquatic organisms is well-documented (Burridge et al 2004 Reynolds et al 2014 Tulbure et al 2014) These environments facilitate spread recruitment and invasion of organisms by providing food (OrsquoSullivan et al 2014) a favourable environment during a shift or an unfavourable time period (Hannah et al 2014) and reducing the distance between suitable habitats for organisms with a mobile life stage (Gaines and Bertness 1992) Perhaps not all these factors are necessary For example habitats with unstable environmental characteristics such as stromatolite pools still appear to create suitable stepping stones for habitat generalists such as the estuarine tubeworm

Ficopomatus enigmaticus exhibits gregarious larval settlement which is strongly affected by the ability of the larvae to recognise adults of their own species (Bianchi and Morri 1996) the nature of the settlement substrate and water flow velocity (Kupriyanova et al 2001) Due to their position and physical structure stromatolite pools maintain relatively constant water levels throughout the year and appear to provide a degree of shelter against strong currents that would disrupt larval settlement In agreement with Thorp (1994) the shallow depth of invaded pools led to the development of elevated temperatures during the reproductive period of F enigmaticus within the stromatolites thereby enhancing larval and adult growth Indeed invaded pools may reach higher temperatures than uninvaded pools and the ocean during which time worm growth could escalate Furthermore when over 95 of the population died in invaded pools in February 2014 a small portion of the population survived and persisted during the entire study period in certain stromatolite pools which acted as refuges for F enigmaticus The cause of the demise of F enigmaticus in February is not certain but was possibly linked to a harmful algal bloom prevailing in the area at that time Red tides can cause hypoxic

Figure 4 PCA showing differences in abiotic data collected during 2014 from four invaded and four uninvaded stromatolite pools The PCA is presented with labels for the different seasons (a) and presenceabsence of F enigmaticus (b) The first two axes explain 374 of the total variance (PC1 = 22 and PC2 = 154)

conditions that would have been lethal to F enigma-ticus even though it is tolerant to low dissolved oxygen (Dittmann et al 2009)

Despite its wide salinity and temperature tolerance range environmental conditions do influence growth rates of F enigmaticus (Bianchi and Morri 1996) Rates of tube length growth vary widely (reviewed in Dittmann et al 2009) In this study the fastest F enigmaticus growth rates and greatest abundances were recorded in stromatolite pools during a mass recruitment event at the onset of Austral spring However tube growth was also not significantly different between seasons Furthermore the presence of empty tubes in some pools suggests that worms have survived in greater numbers in the past Post-settlement growth of F enigmaticus juveniles is very fast and particularly affected by salinity and

NAF Miranda et al

264

temperature (Dittmann et al 2009 and references therein) Once individuals settle they can grow to maturity lengths of 6ndash10 mm in a few weeks although this may vary regionally However temperatures exceeding 20ordmC and salinities of 10ndash30 appear to be optimal for F enigmaticus growth (Tebble 1953) Ficopomatus enigmaticus is sensitive to reductions in temperature (Kupriyanova et al 2001) and as with most invertebrates embryonic and larval development time increases with decreasing temperatures (Kupriyanova et al 2001) The minimum temperature value for spawning can vary among populations and is reported to range from 10 to 17degC (Dittmann et al 2009) During the current study average temperatures as low as 145degC were recorded in the ocean in spring while invaded stromatolite pools had average temperatures gt 20degC which seem to be more favourable for growth and reproduction

Ficopomatus enigmaticus larvae are passively distributed by water currents (Kupriyanova et al 2001) and the source of the spawning event that resulted in the early spring recruitment in stromatolite pools is uncertain Perhaps the increase in temperature in pools reduction in swell height and steady rainfall created the required conditions for successful spawning The source of the larvae may have been the persisting population of large adult worms in the stromatolite pools Alternatively F enigmaticus could be introduced through shipping and mariculture (Glasby et al 2007) attached to debris coming from adjacent estuaries with larger populations and even attached to large mobile organisms such as turtles and crabs Although only one period of spawning and settlement was observed in the current study more periods are possible since different populations exhibit variability in settlement periods and reproductive activity seems to be timed to fit the preferred local conditions (Dittmann et al 2009)

As suggested by Hill (1967) for the closely related Ficopomatus uschakovi (Pillai 1960) F enigmaticus may have different salinity optima for survival growth and reproduction The implication is that salinity fluctuations may be critical for the successful reproduction and development of Ficopomatus (Tebble 1953) Fluctuations in temperature and salinity may also exclude competitors and predators of F enigmaticus allowing them to recruit Deeper pools are more stable in terms of temperature but may also be harder to colonize due to biotic barriers such as increased algal growth competition and predation Limitations on potential settlement substrates can result in the use of any available surfaces including roots or other decomposing plant material which is not ideal as the worms are bound to be dislodged Dislodging may also happen when

worms settle on brittle stromatolite deposits However they may persist for long enough to attract other worms and spawn High rates of predation by crabs and molluscs combined with increased competition for food and space with other benthic organisms may explain the absence of F enigmaticus in lower pools (excluded from analyses in this study) Although only environmental variables were considered in this study biotic factors are also important and should be addressed in future studies

The filter-feeding ability of F enigmaticus is remarkable as it can affect whole ecosystems by removing large amounts of particulate matter from the water column thus affecting primary production by removing phytoplankton potentially ameliorating eutrophication and decreasing overall turbidity (Davies et al 1989 Bruschetti et al 2008) However the F enigmaticus population densities in stromatolite pools are much lower than those in estuaries and lagoons where they form reefs Based on clearance rate estimates of 859 mlmgminus1 dry mass of worm hminus1 (Davies et al 1989) worms in the current study filtered a maximum of 19 L of water per pool per day Although turbidity TSS POM and chl-a were marginally lower in some invaded pools compared to uninvaded pools it remains inconclusive whether the feeding of F enigmaticus had a significant effect in stromatolite pools

Wasson et al (2001) indicated that F enigmaticus and other invasive species can make use of suitable estuarine habitats as ldquostepping stonesrdquo Interestingly invasive species can be transferred via stepping stone habitats with potentially unfavourable environmental conditions (Apte et al 2000) Land-use changes in the past few decades have resulted in the introduction of more artificial structures in aquatic environments and increased dumping of waste especially buoyant plastic into coastal waters both of which have been linked to global increases in the spread and biomass of F enigmaticus (Schwindt et al 2004b McQuaid and Griffiths 2014) and other invasive aquatic species (Airoldi et al 2015 Mesel et al 2015) According to Saura et al (2013) the capacity of species to exploit stepping stones depends on species-specific life-history traits This study shows that F enigmaticus is capable of using small freshwater seepage areas along the South African coastline Havel et al (2005) and Johnson et al (2008) reported that small reservoirs and dams also can facilitate the spread of invasive species into seemingly isolated habitats Similarly perhaps unique ecosystems such as stromatolite pools which provide suitable settlement surfaces serve as stepping stones for the spread of a variety of organisms along the coast including invasive species

Invasive polychaete in marine stromatolites

265

Acknowledgements

This work was supported by the South African Research Chairs Initiative of the Department of Science and Technology (DST) and National Research Foundation (NRF) of South Africa Any opinion finding and conclusion or recommendation expressed in this document is that of the authors and the NRF does not accept any liability in this regard The authors wish to thank the South African Weather Service for providing climate data Windguru for their swell and wave predictions and the South African Environmental Observation Network (SAEON) for providing hourly underwater temperature data for the inshore environment We are also grateful to the anonymous reviewers and to Ryan Reisinger and Chris Oosthuizen for their constructive input which strengthened the paper

References

Airoldi L Turon X Perkol-Finkel S Rius M (2015) Corridors for aliens but not for natives effects of marine urban sprawl at a regional scale Diversity and Distributions 21 755ndash768 httpdxdoiorg101111ddi12301

Anderson MJ Gorley RN Clarke KR (2008) PERMANOVA+ for PRIMER Guide to software and statistical methods PRIMER-E Plymouth UK

Apte S Holland B Godwin LS Gardner JA (2000) Jumping Ship a stepping stone event mediating transfer of a non-indigenous species via a potentially unsuitable environment Biological Invasions 2 75ndash79 httpdxdoiorg101023A1010024818644

Bax N Williamson A Aguero M Gonzalez E Geeves W (2003) Marine invasive alien species a threat to global biodiversity Emerging Issues in Oceans Coasts and Islands 27 313ndash323 httpdxdoiorg101016s0308-597x(03)00041-1

Bellard C Leroy B Thuiller W Rysman J-F Courchamp F (2016) Major drivers of invasion risks throughout the world Ecosphere 7 e01241 httpdxdoiorg101002ecs21241

Bianchi CN Morri C (2001) The battle is not to the strong serpulid reefs in the lagoon of Orbetello (Tuscany Italy) Estuarine Coastal and Shelf Science 53 215ndash220 httpdxdoiorg101006 ecss20010793

Bianchi CN Morri C (1996) Ficopomatus ldquoReefsrdquo in the Po River Delta (Northern Adriatic) their constructional dynamics biology and influences on the brackish-water biota Marine Ecology 17 51ndash66 httpdxdoiorg101111j1439-04851996tb00489x

Blackburn TM Lockwood JL Cassey P (2015) The influence of numbers on invasion success Molecular Ecology 24 1942ndash1953 httpdxdoiorg101111mec13075

Bosak T Knoll AH Petroff AP (2013) The meaning of stromatolites Annual Review of Earth and Planetary Sciences 41 21ndash44 httpdxdoiorg101146annurev-earth-042711-105327

Bruschetti M Luppi T Fanjul E Rosenthal A Iribarne O (2008) Grazing effect of the invasive reef-forming polychaete Ficopomatus enigmaticus (Fauvel) on phytoplankton biomass in a SW Atlantic coastal lagoon Journal of Experimental Marine Biology and Ecology 354 212ndash219 httpdxdoiorg101016 jjembe200711009

Burnham KP Anderson DR (2002) Model selection and multimodel inference a practical information-theoretical approach 2nd ed Springer-Verlag New York

Burridge CP Hurt AC Farrington LW Coutin PC Austin CM (2004) Stepping stone gene flow in an estuarine-dwelling sparid from south-east Australia Journal of Fish Biology 64 805ndash819 httpdxdoiorg101111j1095-864920040347x

Cooper JAG Smith AM Arnscheidt J (2013) Contemporary stromatolite formation in high intertidal rock pools Giants Causeway Northern Ireland preliminary observations In Conley DC Masselink G Russell PE OHare TJ (eds) Proceedings 12th International Coastal Symposium (Plymouth England) pp 1675ndash1680 httpdxdoiorg102112si65-2831

Davies BR Stuart V de Villiers M (1989) The filtration activity of a serpulid polychaete population Ficopomatus enigmaticus (Fauvel) and its effects on water quality in a coastal marina Estuarine Coastal and Shelf Science 29 613ndash620 httpdxdoiorg 1010160272-7714(89)90014-0

Day JH (1951) The polychaete fauna of South Africa Part I The intertidal and estuarine Polychaeta of Natal and Mozambique Annals of the Natal Museum 12 1ndash67

Day JH (1981) Estuarine ecology with particular reference to southern Africa AA Balkema Publishers Netherlands 441 pp

Dittmann S Rolston A Benger SN Kupriyanova EK (2009) Habitat requirements distribution and colonisation of the tubeworm Ficopomatus enigmaticus in the Lower Lakes and Coorong Report for the South Australian Murray-Darling Basin Natural Resources Management Board Adelaide 99 pp

Forbes M Vogwill R Onton K (2010) A characterisation of the coastal tufa deposits of southndashwest Western Australia Sedimentary Geology 232 52ndash65 httpdxdoiorg101016jsedgeo 201009009

Fornos JJ Forteza V Martinez-Taberner A (1997) Modern poly-chaete reefs in Western Mediterranean lagoons Ficopomatus enigmaticus (Fauvel) in the Albufera of Menorca Balearic Islands Palaeogeography Palaeoclimatology Palaeoecology 128 175ndash186 httpdxdoiorg101016S0031-0182(96)00045-4

Gaines SD Bertness MD (1992) Dispersal of juveniles and variable recruitment in sessile marine species Nature 360 579ndash580 httpdxdoiorg101038360579a0

Gallardo B Clavero M Saacutenchez MI Vilagrave M (2016) Global eco-logical impacts of invasive speices in aquatic ecosystems Global Change Biology 22 151ndash163 httpdxdoiorg101111gcb13004

Glasby T Connell S Holloway M Hewitt C (2007) Nonindigenous biota on artificial structures could habitat creation facilitate biological invasions Marine Biology 151 887ndash895 httpdxdoiorg101007s00227-006-0552-5

Grotzinger JP Knoll AH (1999) Stromatolites in precambrian carbonates evolutionary mileposts or environmental dipsticks Annual Review of Earth and Planetary Sciences 27 313ndash358 httpdxdoiorg101146annurevearth271313

Hannah L Flint L Syphard AD Moritz MA Buckley LB McCullough IM (2014) Fine-grain modeling of species response to climate change holdouts stepping-stones and microrefugia Trends in Ecology and Evolution 29 390ndash397 httpdxdoiorg101016jtree201404006

Havel JE Lee CE Zanden MJV (2005) Do reservoirs facilitate invasions into landscapes BioScience 55 518ndash525 httpdxdoiorg1016410006-3568(2005)055[0518DRFIIL]20CO2

Johnson PTJ Olden JD Zanden MJV (2008) Dam invaders impoundments facilitate biological invasions into freshwaters Frontiers in Ecology and the Environment 6 357ndash363 httpdxdoiorg101890070156

Kupriyanova EK Nishi E ten Hove HA Rzhavsky AV (2001) Life-history patterns in serpulimorph polychaetes ecological and evolutionary perspectives Oceangraphy and Marine Biology an Annual Review 39 1ndash101

Lau JA Schultheis EH (2015) When two invasion hypotheses are better than one New Phytologist 205 958ndash960 httpdxdoiorg 101111nph13260

Legendre P Anderson MJ (1999) Distance-based redundancy analysis testing multi-species responses in multi-factorial ecological experiments Ecological Monographs 69 1ndash24 httpdxdoiorg1018900012-9615(1999)069[0001DBRATM]20CO2

McArdle BH Anderson MJ (2001) Fitting multivariate models to community data a comment on distance-based redundancy analysis Ecology 82 290ndash297 httpdxdoiorg10189000129658(20 01)082[0290FMMTCD]20CO2

McQuaid KA Griffiths CL (2014) Alien reef-building polychaete drives long-term changes in invertebrate biomass and diversity in a small urban estuary Estuarine Coastal and Shelf Science 138 101ndash106 httpdxdoiorg101016jecss201312016

NAF Miranda et al

258

Figure 1 Map of the study area showing the sampling locations on the south coast of South Africa (A B and C) as well as the location of all coastal freshwater seeps in the surrounding area from Cape Recife to Oyster Bay (black dots 540 in total) Two stromatolite pools uninvaded by F enigmaticus were sampled at site A three invaded pools were sampled at site B one invaded and two uninvaded pools were sampled at site C Adapted from Perissinotto et al (2014)

South African stromatolites host a wide variety of freshwater estuarine and marine organisms that appear to alternate their dominance in response to vertical mixing and the balance between freshwater and seawater inputs (Perissinotto et al 2014) Among these species is the invasive estuarine tubeworm Ficopomatus enigmaticus (Fauvel 1923) The species is suspected to originate from temperate regions of the Indian Ocean but geographic origin is still uncertain and a matter of debate (reviewed by Dittmann et al 2009) The species was first recorded in South Africa (as Mercierella enigmatica) in the 1950rsquos (Day 1951) and is thought to have been introduced by ship fouling from southern or western Australia (Mead et al 2011a) Presently most estuaries in South Africa are colonised by this alien species (Day 1981 Plisko and Griffiths 2011) and it is suspected that stromatolite pools act as stepping-stones in the spread of this species across estuarine systems that are often located far apart from each other This serpulid tubeworm is considered to be a highly invasive ecosystem engineer that has colonised many subtropical and temperate areas of the world (ten Hove and Weerdenburg 1978 Day 1981 Fornos et al 1997 Bianchi and Morri 2001 Mead et al 2011b Pernet et al 2016) It builds large reefs on hard

substrates including artificial structures and has had major impacts on the ecology of systems it invaded in Argentina and South Africa (Obenat and Pezzani 1994 Schwindt and Iribarne 2000 Bianchi and Morri 2001 Schwindt et al 2001 Schwindt et al 2004a Schwindt et al 2004b Dittmann et al 2009 McQuaid and Griffiths 2014)

This study represents the first report of an invasive species associated with living stromatolites Modern stromatolites along the South African coast are characterised by highly variable environmental conditions with frequent and extreme fluctuations associated with regular spring tidal over-topping and flushing with freshwater from groundwater (Perissinotto et al 2014) This high variability creates a unique habitat suited only to those species able to tolerate extreme environmental fluctuations Our goal was to examine the presence and potential impacts of the reef-forming tubeworm F enigmaticus in stromatolite ecosystems This was done by assessing population abundance patterns and growth rates of the tubeworm in stromatolite pools to determine the most important environmental variables correlated to tubeworm populations by comparing invaded and uninvaded habitats in terms of environmental variables

Invasive polychaete in marine stromatolites

259

Table 1 Stromatolite pools sampled on the south coast of South Africa Eight pools were surveyed in total four invaded and four uninvaded by Ficopomatus enigmaticus

Pools Pool number Site Status

Three upper pools (sensu Perissinotto et al 2014) contained stromatolite structures and were located nearest to freshwater seepage points

1 A Uninvaded by F enigmaticus

2 B Invaded by F enigmaticus

3 C Uninvaded by F enigmaticus

Three middle pools contained the most stromatolite accretion and are considered typical barrage pools (Perissinotto et al 2014) They were located between seepage points and the subtidal zone

4 A Uninvaded by F enigmaticus

5 B Invaded by F enigmaticus

6 C Uninvaded by F enigmaticus

Two additional pools were situated nearer to seepage points than the subtidal zone These contained stromatolite structures and relatively high numbers of live F enigmaticus as well as empty tubes attached to boulders

7 B Invaded by F enigmaticus

8 C Invaded by F enigmaticus

Methods

Study sites and sample collection

Samples were collected in 2014 during the first extensive survey of the three barrage pool sites reported by Perissinotto et al (2014) Collection sites were located west of Cape Recife (site A 34ordm02prime4213PrimeS 25ordm34prime0750PrimeE) at Schoenmakerskop (site B 34ordm02prime 2823PrimeS 25ordm32prime1860PrimeE) and east of Seaview (site C 34ordm01prime0316PrimeS 25ordm21prime5648PrimeE) along the South African coastline in the vicinity of Port Elizabeth (Figure 1) Sampling was conducted at lowest low-tide during the first spring tidal phase of each month during each season (autumn Mar ndash May winter Jun ndash Aug spring Sep ndash Nov summer Dec ndash Feb)

The current study focused on middle and upper pools in sites A B and C (see Perissinotto et al 2014) as well as two additional pools one at site B and one at site C (Figure 1 Table 1) All pools in this study were located between the subtidal waterline and landward groundwater seepage Lower pools (sensu Perissinotto et al 2014) were closest to the subtidal had the least stromatolite growth and always contained marine organisms with no trace of F enigmaticus Therefore lower pools were not included in this study

A YSI 6600-V2 multiprobe system (YSI Incorporated Yellow Springs Ohio USA) was used to measure physico-chemical parameters in all pools temperature (degC) salinity depth (m) pH turbidity (NTU) and dissolved oxygen (DO mgl-1) Star Oddi DST CT (httpwwwstar-oddicom) probes were deployed in crevices at the bottom of each middle pool and

recorded hourly temperature and salinity data Additional information that influences all pools was also collected for the study area Rainfall as measured by the South African Weather Services at the Port Elizabeth International Airport (~ 9 km from Site B) influences freshwater input to all the pools Swell height as modelled by Windguru (httpwwwwindgurucz) for Port Elizabeth was considered an indicator of environmental energy as the pools are regularly over-topped by saltwater during spring high tides and storm surges Inshore ocean surface temperature was measured using Onset Hoboreg U22-001 underwater temperature recorders (Onset Cape Cod Massa-chusetts USA) deployed at depths lt 1 m below mean spring low water Ficopomatus enigmaticus are suspension feeders known to filter large volumes of water (Davies et al 1989) hence potentially affecting total suspended solids (TSS) particulate organic matter (POM) and chlorophyll-a (chl-a) concentra-tions Water samples were collected monthly from pools to determine TSS (mgl-1) POM (mgl-1) and chl-a (mgm-3) Water was filtered through pre-combusted and pre-weighed Whatman GFF filters Filters with retained materials were oven dried (60degC for 48 h) and weighed with a digital balance (001 mg) to determine TSS (total dry mass) and then combus-ted (450degC for 4 h) and weighed again to determine POM (organic component) For water-column chl-a analyses water was filtered through a GFF filter To extract pigments filters with retained material were placed in 8 ml of 90 acetone solution for 48 h in darkness at 4degC Fluorescence was measured using a Turner 10-AU narrow-band system (Turner Designs Sunnyvale California USA)

NAF Miranda et al

260

The availability of substrates suitable for colonisation by F enigmaticus was estimated every month Objects larger than 500 cm3 (such as bottles cans tree trunks and other debris) were regarded as substrates on which F enigmaticus could settle (Schwindt and Iribarne 2000 Schwindt et al 2004a) and were counted in each pool Algal mats can cover hard substrates and effectively create a physical barrier to larval settlement (Norkko and Bonsdorff 1996) Therefore to calculate the total (algae-free) area potentially available for the settlement of F enigmaticus during this study the total hard substrate area of each pool was measured and the percentage benthic algal cover was estimated based on photo-quadrats A 12 megapixel digital camera was positioned 15 m over a 1 times 1 m PVC quadrat which was placed on the water surface and aligned according to landmarks The entire water surface of pools was photographed every month in this way

All pools were searched for traces of tubeworms every month The number of live F enigmaticus individuals was counted in each pool and the length of their calcareous tubes was measured with Vernier callipers (to the nearest 001 mm) Tube growth (increase in length mm) was also tracked for each live individual worm found Photographs were used to confirm the identity of individuals as each displayed distinct settlement locations and tube shapes Measurements were repeated every 30 days and used to determine tube length increases of individual worms Average monthly tube growth rate (increase in length) was then calculated for invaded pools To determine dry mass (biomass) worms (5 individuals per pool) were separated from their tubes oven dried (60degC for 48 h) and individually weighed to the nearest 001 mg

Statistical analyses

General linear models (GLM) with quasi-Poisson distribution (season four levels autumn winter spring summer status two levels invaded and uninvaded) were run for each environmental variable (TSS POM chl-a temperature salinity depth pH turbidity dissolved oxygen potential available area for settlement potential substrates for settlement) followed by Tukeyrsquos post-hoc testing to determine if there were significant differences between invaded and uninvaded pools in each season ANOVA followed by Tukeyrsquos post-hoc test was used to determine if there were differences between seasons in log(x+1) transformed F enigmaticus tube growth data In both cases all model assumptions were met These analyses were done using the statistical software R version 2151

Figure 2 Ficopomatus enigmaticus tubeworms on colloform formations in a stromatolite pool along the south coast of South Africa (a) ventral view (b) dorsal view (c) and operculum (d) of extracted specimen Photographs by NAF Miranda

Non-parametric permutational MANOVA (PERMANOVA Anderson et al 2008) was used to test for differences in the measured environmental variables In this regard a three-way PERMANOVA design tested for differences between pools uninvaded and invaded (UI) by F enigmaticus (fixed term 2 levels) pools (random factor nested in UI 8 levels) and seasons (fixed factor four levels) The resemblance matrix was based on Euclidean distance Statistical significance was tested using 9999 permutations of residuals under a reduced model Distance-based linear modelling (DISTLM Legendre and Anderson 1999 McArdle and Anderson 2001 Anderson et al 2008) was used to perform permuta-tional regression (9999 random permutations) to test for linear relationships between F enigmaticus abundance (response) and the above-mentioned environmental variables (predictors) The response variable (F enigmaticus abundance) was first converted to a Euclidean distance matrix A step-wise selection procedure was used incorporating the corrected Akaike Information Criterion (AICc) (Burnham and Anderson 2002) as the selection criterion to measure the relative goodness of fit for each model The final subset of environmental variables that provided maximum parsimony (according to the AICc criterion) is presented The a priori significance level (α) for all multivariate tests was set at 001

Invasive polychaete in marine stromatolites

261

Figure 3 Rainfall ocean temperature and swell height data collected in the study area (a-c) selected environmental variables (water temperature salinity available potential area for settlement and pool depth) collected from four stromatolite pools invaded by F enigmaticus (red solid line) and four uninvaded pools (blue dashed line) (d-g) monthly F enigmaticus tube growth in invaded pools (h) and number of F enigmaticus individuals (abundance) per invaded pool (i) Data were collected in 2014 and are presented as monthly means (plusmn SD)

Results

The highest mean TSS and POM values were recorded during summer (supplementary material Table S1) The lowest mean TSS was recorded during spring The lowest mean POM highest mean turbidity and highest mean chl-a were recorded during autumn Temperature was lowest in winter and highest in summer (Table S1 Figure 3) In general all pools were colder and saltier in autumn and winter and warmer and fresher in spring and summer Mean DO ranged between 8 and 12 mgl-1 and mean pH was approximately 8 in all pools While both invaded and uninvaded pools had areas potentially available for settlement throughout the year (Table S1 Figure 3) these were significantly smaller only in uninvaded pools during winter

The density of F enigmaticus was greatest in spring reaching mean (plusmn SE) values of 146 plusmn 130 indm-2

(Table S1) During summer the average increase in tube length reached 686 mm per 30 days (Figure 3) However there were no significant differences in tube growth between seasons (ANOVA P gt 005) Individuals had an average dry mass of 023 plusmn 004 mg tube length of 2145 plusmn 216 mm and reached a biomass of up to 9435 mg dry mass per invaded pool (or 2359 mg m-2) After a mass-mortality event at the end of January 2014 (coinciding with a red tide in the Algoa Bay area and the lowest DO readings recorded in the study) no live F enigmaticus individuals were recorded in 3 of the invaded pools (site C additional pool site B upper and additional pool) from February to August However a few large individuals (average biomass 075 plusmn 002 mg and tube length 2786 plusmn 047 mm) persisted in a single pool (middle pool site B) during autumn and winter (total dry mass 747 mg or 062 mgm-2)

NAF Miranda et al

262

Table 2 PERMANOVA test for differences in abiotic variables across F enigmaticus invaded and uninvaded stromatolite pools (IU fixed factor) pools (random factor nested in IU) and seasons (fixed factor) The degrees of freedom df sum of squares SS means squared MS pseudo ndash F statistic and probability level based on 9999 random permutations P(perm) are presented Significant factors are in bold (α = 001) Data were collected in Eastern Cape stromatolite pools in 2014

Source df SS MS Pseudo-F P(perm)

IU 1 39382 394 0606 0778

Seasons 3 22744 758 8440 0001

Pools (IU) 6 39007 650 8488 0001

IU times Seasons 3 21214 71 0787 0754

Pools(IU) times Seasons 18 16169 90 1173 0093

Residuals 64 4902 77 0606 0778

Total 95 1330

Table 3 Distance-based linear regression model of F enigmaticus abundance (response) against environmental variables (predictors) measured in Eastern Cape stromatolite pools in 2014 (A) Sequential tests for stepwise model (R2 = 026) and percentage of multivariate variation explained by individual axes are presented (B) The most parsimonious model included number of potential substrates for settlement ldquoSubstratesrdquo stromatolite pool water temperature ldquoTemprdquo and available potential area for settlement ldquoAreardquo

A Model summary

Variable AICc SS (trace) Pseudo - F P Prop Cumul res df

Substrates 62640 78690 1180 lt 001 0111 0111 94

Temp (degC) 62095 47619 764 lt 001 0068 0179 93

Area (m2) 61357 54886 963 lt 001 0078 0257 92 B Variation explained by axes

Axis Individual Cumulative Individual Cumulative

explained variation of fitted model explained variation of total variation

1 9821 9821 2521 2521

2 179 100 046 2567

Mean ocean surface temperature was lowest in spring and highest in summer (January and February) (Figure 3) Mean swell height increased in autumn and peaked in winter with this peak coinciding with an increase in mean salinity recorded in all pools in winter while the highest salinities were recorded in invaded pools (Table S1 Figure 3) There was a clear recruitment event at the onset of spring (AugustSeptember) during which 95 plusmn 49 individuals were recorded per invaded pool (Table S1 Figure 3) This coincided with an increase in mean rainfall (gt 50 mm) and a drop in mean swell height at the end of winter (mean swell height remained at approximately 3 m from August to December)

Significant differences in stromatolite pool abiotic data were detected between seasons and pools (Table 2) No significant differences in abiotic conditions were detected however between invaded and uninvaded pools There were differences among seasons and F enigmaticus presence was greater in spring when temperature TSS and POM were higher in the pools

while swell height was lower and ocean temperature was higher in the study area (Figure 4) The stepwise AICc analysis showed that F enigmaticus abundance exhibited a significant relationship with pool tempera-ture number of substrates and area potentially available for settlement (Table 3) However this three variable model only explained 26 of the total variation in F enigmaticus abundance data

Discussion

Ficopomatus enigmaticus is not an obligate reef builder (Bianchi and Morri 2001) and occurs indivi-dually or in small aggregations in the South African stromatolite pools often attached to rocks directly on stromatolites (Figure 2) or on any other available substrates Availability of settlement substrates and water temperature appear to be the most important variables controlling the persistence of F enigmaticus in stromatolite pools Overall environmental variables explained a low percentage of the variation in F enigmaticus abundance (Table 3) This is expected

Invasive polychaete in marine stromatolites

263

for a habitat generalist with wide environmental tolerance However Schwindt et al (2004a) argued that habitats favoured by F enigmaticus populations are very similar in their physical chemical and biological characteristics throughout the world These authors also suggested that the most important variables that affect the spread of this species in invaded habitats may be salinity nutrients (ie TSS POM and chl-a) and environmental energy (eg current speed or swell height as proxy) The TSS POM and chl-a values measured in the current study correspond with the lowest recorded by Schwindt et al (2004a) and therefore may partially explain the relatively small population size observed in stromatolite pools

The use of estuaries and intermittent water bodies as stepping stones for aquatic organisms is well-documented (Burridge et al 2004 Reynolds et al 2014 Tulbure et al 2014) These environments facilitate spread recruitment and invasion of organisms by providing food (OrsquoSullivan et al 2014) a favourable environment during a shift or an unfavourable time period (Hannah et al 2014) and reducing the distance between suitable habitats for organisms with a mobile life stage (Gaines and Bertness 1992) Perhaps not all these factors are necessary For example habitats with unstable environmental characteristics such as stromatolite pools still appear to create suitable stepping stones for habitat generalists such as the estuarine tubeworm

Ficopomatus enigmaticus exhibits gregarious larval settlement which is strongly affected by the ability of the larvae to recognise adults of their own species (Bianchi and Morri 1996) the nature of the settlement substrate and water flow velocity (Kupriyanova et al 2001) Due to their position and physical structure stromatolite pools maintain relatively constant water levels throughout the year and appear to provide a degree of shelter against strong currents that would disrupt larval settlement In agreement with Thorp (1994) the shallow depth of invaded pools led to the development of elevated temperatures during the reproductive period of F enigmaticus within the stromatolites thereby enhancing larval and adult growth Indeed invaded pools may reach higher temperatures than uninvaded pools and the ocean during which time worm growth could escalate Furthermore when over 95 of the population died in invaded pools in February 2014 a small portion of the population survived and persisted during the entire study period in certain stromatolite pools which acted as refuges for F enigmaticus The cause of the demise of F enigmaticus in February is not certain but was possibly linked to a harmful algal bloom prevailing in the area at that time Red tides can cause hypoxic

Figure 4 PCA showing differences in abiotic data collected during 2014 from four invaded and four uninvaded stromatolite pools The PCA is presented with labels for the different seasons (a) and presenceabsence of F enigmaticus (b) The first two axes explain 374 of the total variance (PC1 = 22 and PC2 = 154)

conditions that would have been lethal to F enigma-ticus even though it is tolerant to low dissolved oxygen (Dittmann et al 2009)

Despite its wide salinity and temperature tolerance range environmental conditions do influence growth rates of F enigmaticus (Bianchi and Morri 1996) Rates of tube length growth vary widely (reviewed in Dittmann et al 2009) In this study the fastest F enigmaticus growth rates and greatest abundances were recorded in stromatolite pools during a mass recruitment event at the onset of Austral spring However tube growth was also not significantly different between seasons Furthermore the presence of empty tubes in some pools suggests that worms have survived in greater numbers in the past Post-settlement growth of F enigmaticus juveniles is very fast and particularly affected by salinity and

NAF Miranda et al

264

temperature (Dittmann et al 2009 and references therein) Once individuals settle they can grow to maturity lengths of 6ndash10 mm in a few weeks although this may vary regionally However temperatures exceeding 20ordmC and salinities of 10ndash30 appear to be optimal for F enigmaticus growth (Tebble 1953) Ficopomatus enigmaticus is sensitive to reductions in temperature (Kupriyanova et al 2001) and as with most invertebrates embryonic and larval development time increases with decreasing temperatures (Kupriyanova et al 2001) The minimum temperature value for spawning can vary among populations and is reported to range from 10 to 17degC (Dittmann et al 2009) During the current study average temperatures as low as 145degC were recorded in the ocean in spring while invaded stromatolite pools had average temperatures gt 20degC which seem to be more favourable for growth and reproduction

Ficopomatus enigmaticus larvae are passively distributed by water currents (Kupriyanova et al 2001) and the source of the spawning event that resulted in the early spring recruitment in stromatolite pools is uncertain Perhaps the increase in temperature in pools reduction in swell height and steady rainfall created the required conditions for successful spawning The source of the larvae may have been the persisting population of large adult worms in the stromatolite pools Alternatively F enigmaticus could be introduced through shipping and mariculture (Glasby et al 2007) attached to debris coming from adjacent estuaries with larger populations and even attached to large mobile organisms such as turtles and crabs Although only one period of spawning and settlement was observed in the current study more periods are possible since different populations exhibit variability in settlement periods and reproductive activity seems to be timed to fit the preferred local conditions (Dittmann et al 2009)

As suggested by Hill (1967) for the closely related Ficopomatus uschakovi (Pillai 1960) F enigmaticus may have different salinity optima for survival growth and reproduction The implication is that salinity fluctuations may be critical for the successful reproduction and development of Ficopomatus (Tebble 1953) Fluctuations in temperature and salinity may also exclude competitors and predators of F enigmaticus allowing them to recruit Deeper pools are more stable in terms of temperature but may also be harder to colonize due to biotic barriers such as increased algal growth competition and predation Limitations on potential settlement substrates can result in the use of any available surfaces including roots or other decomposing plant material which is not ideal as the worms are bound to be dislodged Dislodging may also happen when

worms settle on brittle stromatolite deposits However they may persist for long enough to attract other worms and spawn High rates of predation by crabs and molluscs combined with increased competition for food and space with other benthic organisms may explain the absence of F enigmaticus in lower pools (excluded from analyses in this study) Although only environmental variables were considered in this study biotic factors are also important and should be addressed in future studies

The filter-feeding ability of F enigmaticus is remarkable as it can affect whole ecosystems by removing large amounts of particulate matter from the water column thus affecting primary production by removing phytoplankton potentially ameliorating eutrophication and decreasing overall turbidity (Davies et al 1989 Bruschetti et al 2008) However the F enigmaticus population densities in stromatolite pools are much lower than those in estuaries and lagoons where they form reefs Based on clearance rate estimates of 859 mlmgminus1 dry mass of worm hminus1 (Davies et al 1989) worms in the current study filtered a maximum of 19 L of water per pool per day Although turbidity TSS POM and chl-a were marginally lower in some invaded pools compared to uninvaded pools it remains inconclusive whether the feeding of F enigmaticus had a significant effect in stromatolite pools

Wasson et al (2001) indicated that F enigmaticus and other invasive species can make use of suitable estuarine habitats as ldquostepping stonesrdquo Interestingly invasive species can be transferred via stepping stone habitats with potentially unfavourable environmental conditions (Apte et al 2000) Land-use changes in the past few decades have resulted in the introduction of more artificial structures in aquatic environments and increased dumping of waste especially buoyant plastic into coastal waters both of which have been linked to global increases in the spread and biomass of F enigmaticus (Schwindt et al 2004b McQuaid and Griffiths 2014) and other invasive aquatic species (Airoldi et al 2015 Mesel et al 2015) According to Saura et al (2013) the capacity of species to exploit stepping stones depends on species-specific life-history traits This study shows that F enigmaticus is capable of using small freshwater seepage areas along the South African coastline Havel et al (2005) and Johnson et al (2008) reported that small reservoirs and dams also can facilitate the spread of invasive species into seemingly isolated habitats Similarly perhaps unique ecosystems such as stromatolite pools which provide suitable settlement surfaces serve as stepping stones for the spread of a variety of organisms along the coast including invasive species

Invasive polychaete in marine stromatolites

265

Acknowledgements

This work was supported by the South African Research Chairs Initiative of the Department of Science and Technology (DST) and National Research Foundation (NRF) of South Africa Any opinion finding and conclusion or recommendation expressed in this document is that of the authors and the NRF does not accept any liability in this regard The authors wish to thank the South African Weather Service for providing climate data Windguru for their swell and wave predictions and the South African Environmental Observation Network (SAEON) for providing hourly underwater temperature data for the inshore environment We are also grateful to the anonymous reviewers and to Ryan Reisinger and Chris Oosthuizen for their constructive input which strengthened the paper

References

Airoldi L Turon X Perkol-Finkel S Rius M (2015) Corridors for aliens but not for natives effects of marine urban sprawl at a regional scale Diversity and Distributions 21 755ndash768 httpdxdoiorg101111ddi12301

Anderson MJ Gorley RN Clarke KR (2008) PERMANOVA+ for PRIMER Guide to software and statistical methods PRIMER-E Plymouth UK

Apte S Holland B Godwin LS Gardner JA (2000) Jumping Ship a stepping stone event mediating transfer of a non-indigenous species via a potentially unsuitable environment Biological Invasions 2 75ndash79 httpdxdoiorg101023A1010024818644

Bax N Williamson A Aguero M Gonzalez E Geeves W (2003) Marine invasive alien species a threat to global biodiversity Emerging Issues in Oceans Coasts and Islands 27 313ndash323 httpdxdoiorg101016s0308-597x(03)00041-1

Bellard C Leroy B Thuiller W Rysman J-F Courchamp F (2016) Major drivers of invasion risks throughout the world Ecosphere 7 e01241 httpdxdoiorg101002ecs21241

Bianchi CN Morri C (2001) The battle is not to the strong serpulid reefs in the lagoon of Orbetello (Tuscany Italy) Estuarine Coastal and Shelf Science 53 215ndash220 httpdxdoiorg101006 ecss20010793

Bianchi CN Morri C (1996) Ficopomatus ldquoReefsrdquo in the Po River Delta (Northern Adriatic) their constructional dynamics biology and influences on the brackish-water biota Marine Ecology 17 51ndash66 httpdxdoiorg101111j1439-04851996tb00489x

Blackburn TM Lockwood JL Cassey P (2015) The influence of numbers on invasion success Molecular Ecology 24 1942ndash1953 httpdxdoiorg101111mec13075

Bosak T Knoll AH Petroff AP (2013) The meaning of stromatolites Annual Review of Earth and Planetary Sciences 41 21ndash44 httpdxdoiorg101146annurev-earth-042711-105327

Bruschetti M Luppi T Fanjul E Rosenthal A Iribarne O (2008) Grazing effect of the invasive reef-forming polychaete Ficopomatus enigmaticus (Fauvel) on phytoplankton biomass in a SW Atlantic coastal lagoon Journal of Experimental Marine Biology and Ecology 354 212ndash219 httpdxdoiorg101016 jjembe200711009

Burnham KP Anderson DR (2002) Model selection and multimodel inference a practical information-theoretical approach 2nd ed Springer-Verlag New York

Burridge CP Hurt AC Farrington LW Coutin PC Austin CM (2004) Stepping stone gene flow in an estuarine-dwelling sparid from south-east Australia Journal of Fish Biology 64 805ndash819 httpdxdoiorg101111j1095-864920040347x

Cooper JAG Smith AM Arnscheidt J (2013) Contemporary stromatolite formation in high intertidal rock pools Giants Causeway Northern Ireland preliminary observations In Conley DC Masselink G Russell PE OHare TJ (eds) Proceedings 12th International Coastal Symposium (Plymouth England) pp 1675ndash1680 httpdxdoiorg102112si65-2831

Davies BR Stuart V de Villiers M (1989) The filtration activity of a serpulid polychaete population Ficopomatus enigmaticus (Fauvel) and its effects on water quality in a coastal marina Estuarine Coastal and Shelf Science 29 613ndash620 httpdxdoiorg 1010160272-7714(89)90014-0

Day JH (1951) The polychaete fauna of South Africa Part I The intertidal and estuarine Polychaeta of Natal and Mozambique Annals of the Natal Museum 12 1ndash67

Day JH (1981) Estuarine ecology with particular reference to southern Africa AA Balkema Publishers Netherlands 441 pp

Dittmann S Rolston A Benger SN Kupriyanova EK (2009) Habitat requirements distribution and colonisation of the tubeworm Ficopomatus enigmaticus in the Lower Lakes and Coorong Report for the South Australian Murray-Darling Basin Natural Resources Management Board Adelaide 99 pp

Forbes M Vogwill R Onton K (2010) A characterisation of the coastal tufa deposits of southndashwest Western Australia Sedimentary Geology 232 52ndash65 httpdxdoiorg101016jsedgeo 201009009

Fornos JJ Forteza V Martinez-Taberner A (1997) Modern poly-chaete reefs in Western Mediterranean lagoons Ficopomatus enigmaticus (Fauvel) in the Albufera of Menorca Balearic Islands Palaeogeography Palaeoclimatology Palaeoecology 128 175ndash186 httpdxdoiorg101016S0031-0182(96)00045-4

Gaines SD Bertness MD (1992) Dispersal of juveniles and variable recruitment in sessile marine species Nature 360 579ndash580 httpdxdoiorg101038360579a0

Gallardo B Clavero M Saacutenchez MI Vilagrave M (2016) Global eco-logical impacts of invasive speices in aquatic ecosystems Global Change Biology 22 151ndash163 httpdxdoiorg101111gcb13004

Glasby T Connell S Holloway M Hewitt C (2007) Nonindigenous biota on artificial structures could habitat creation facilitate biological invasions Marine Biology 151 887ndash895 httpdxdoiorg101007s00227-006-0552-5

Grotzinger JP Knoll AH (1999) Stromatolites in precambrian carbonates evolutionary mileposts or environmental dipsticks Annual Review of Earth and Planetary Sciences 27 313ndash358 httpdxdoiorg101146annurevearth271313

Hannah L Flint L Syphard AD Moritz MA Buckley LB McCullough IM (2014) Fine-grain modeling of species response to climate change holdouts stepping-stones and microrefugia Trends in Ecology and Evolution 29 390ndash397 httpdxdoiorg101016jtree201404006

Havel JE Lee CE Zanden MJV (2005) Do reservoirs facilitate invasions into landscapes BioScience 55 518ndash525 httpdxdoiorg1016410006-3568(2005)055[0518DRFIIL]20CO2

Johnson PTJ Olden JD Zanden MJV (2008) Dam invaders impoundments facilitate biological invasions into freshwaters Frontiers in Ecology and the Environment 6 357ndash363 httpdxdoiorg101890070156

Kupriyanova EK Nishi E ten Hove HA Rzhavsky AV (2001) Life-history patterns in serpulimorph polychaetes ecological and evolutionary perspectives Oceangraphy and Marine Biology an Annual Review 39 1ndash101

Lau JA Schultheis EH (2015) When two invasion hypotheses are better than one New Phytologist 205 958ndash960 httpdxdoiorg 101111nph13260

Legendre P Anderson MJ (1999) Distance-based redundancy analysis testing multi-species responses in multi-factorial ecological experiments Ecological Monographs 69 1ndash24 httpdxdoiorg1018900012-9615(1999)069[0001DBRATM]20CO2

McArdle BH Anderson MJ (2001) Fitting multivariate models to community data a comment on distance-based redundancy analysis Ecology 82 290ndash297 httpdxdoiorg10189000129658(20 01)082[0290FMMTCD]20CO2

McQuaid KA Griffiths CL (2014) Alien reef-building polychaete drives long-term changes in invertebrate biomass and diversity in a small urban estuary Estuarine Coastal and Shelf Science 138 101ndash106 httpdxdoiorg101016jecss201312016

Invasive polychaete in marine stromatolites

259

Table 1 Stromatolite pools sampled on the south coast of South Africa Eight pools were surveyed in total four invaded and four uninvaded by Ficopomatus enigmaticus

Pools Pool number Site Status

Three upper pools (sensu Perissinotto et al 2014) contained stromatolite structures and were located nearest to freshwater seepage points

1 A Uninvaded by F enigmaticus

2 B Invaded by F enigmaticus

3 C Uninvaded by F enigmaticus

Three middle pools contained the most stromatolite accretion and are considered typical barrage pools (Perissinotto et al 2014) They were located between seepage points and the subtidal zone

4 A Uninvaded by F enigmaticus

5 B Invaded by F enigmaticus

6 C Uninvaded by F enigmaticus

Two additional pools were situated nearer to seepage points than the subtidal zone These contained stromatolite structures and relatively high numbers of live F enigmaticus as well as empty tubes attached to boulders

7 B Invaded by F enigmaticus

8 C Invaded by F enigmaticus

Methods

Study sites and sample collection

Samples were collected in 2014 during the first extensive survey of the three barrage pool sites reported by Perissinotto et al (2014) Collection sites were located west of Cape Recife (site A 34ordm02prime4213PrimeS 25ordm34prime0750PrimeE) at Schoenmakerskop (site B 34ordm02prime 2823PrimeS 25ordm32prime1860PrimeE) and east of Seaview (site C 34ordm01prime0316PrimeS 25ordm21prime5648PrimeE) along the South African coastline in the vicinity of Port Elizabeth (Figure 1) Sampling was conducted at lowest low-tide during the first spring tidal phase of each month during each season (autumn Mar ndash May winter Jun ndash Aug spring Sep ndash Nov summer Dec ndash Feb)

The current study focused on middle and upper pools in sites A B and C (see Perissinotto et al 2014) as well as two additional pools one at site B and one at site C (Figure 1 Table 1) All pools in this study were located between the subtidal waterline and landward groundwater seepage Lower pools (sensu Perissinotto et al 2014) were closest to the subtidal had the least stromatolite growth and always contained marine organisms with no trace of F enigmaticus Therefore lower pools were not included in this study

A YSI 6600-V2 multiprobe system (YSI Incorporated Yellow Springs Ohio USA) was used to measure physico-chemical parameters in all pools temperature (degC) salinity depth (m) pH turbidity (NTU) and dissolved oxygen (DO mgl-1) Star Oddi DST CT (httpwwwstar-oddicom) probes were deployed in crevices at the bottom of each middle pool and

recorded hourly temperature and salinity data Additional information that influences all pools was also collected for the study area Rainfall as measured by the South African Weather Services at the Port Elizabeth International Airport (~ 9 km from Site B) influences freshwater input to all the pools Swell height as modelled by Windguru (httpwwwwindgurucz) for Port Elizabeth was considered an indicator of environmental energy as the pools are regularly over-topped by saltwater during spring high tides and storm surges Inshore ocean surface temperature was measured using Onset Hoboreg U22-001 underwater temperature recorders (Onset Cape Cod Massa-chusetts USA) deployed at depths lt 1 m below mean spring low water Ficopomatus enigmaticus are suspension feeders known to filter large volumes of water (Davies et al 1989) hence potentially affecting total suspended solids (TSS) particulate organic matter (POM) and chlorophyll-a (chl-a) concentra-tions Water samples were collected monthly from pools to determine TSS (mgl-1) POM (mgl-1) and chl-a (mgm-3) Water was filtered through pre-combusted and pre-weighed Whatman GFF filters Filters with retained materials were oven dried (60degC for 48 h) and weighed with a digital balance (001 mg) to determine TSS (total dry mass) and then combus-ted (450degC for 4 h) and weighed again to determine POM (organic component) For water-column chl-a analyses water was filtered through a GFF filter To extract pigments filters with retained material were placed in 8 ml of 90 acetone solution for 48 h in darkness at 4degC Fluorescence was measured using a Turner 10-AU narrow-band system (Turner Designs Sunnyvale California USA)

NAF Miranda et al

260

The availability of substrates suitable for colonisation by F enigmaticus was estimated every month Objects larger than 500 cm3 (such as bottles cans tree trunks and other debris) were regarded as substrates on which F enigmaticus could settle (Schwindt and Iribarne 2000 Schwindt et al 2004a) and were counted in each pool Algal mats can cover hard substrates and effectively create a physical barrier to larval settlement (Norkko and Bonsdorff 1996) Therefore to calculate the total (algae-free) area potentially available for the settlement of F enigmaticus during this study the total hard substrate area of each pool was measured and the percentage benthic algal cover was estimated based on photo-quadrats A 12 megapixel digital camera was positioned 15 m over a 1 times 1 m PVC quadrat which was placed on the water surface and aligned according to landmarks The entire water surface of pools was photographed every month in this way

All pools were searched for traces of tubeworms every month The number of live F enigmaticus individuals was counted in each pool and the length of their calcareous tubes was measured with Vernier callipers (to the nearest 001 mm) Tube growth (increase in length mm) was also tracked for each live individual worm found Photographs were used to confirm the identity of individuals as each displayed distinct settlement locations and tube shapes Measurements were repeated every 30 days and used to determine tube length increases of individual worms Average monthly tube growth rate (increase in length) was then calculated for invaded pools To determine dry mass (biomass) worms (5 individuals per pool) were separated from their tubes oven dried (60degC for 48 h) and individually weighed to the nearest 001 mg

Statistical analyses

General linear models (GLM) with quasi-Poisson distribution (season four levels autumn winter spring summer status two levels invaded and uninvaded) were run for each environmental variable (TSS POM chl-a temperature salinity depth pH turbidity dissolved oxygen potential available area for settlement potential substrates for settlement) followed by Tukeyrsquos post-hoc testing to determine if there were significant differences between invaded and uninvaded pools in each season ANOVA followed by Tukeyrsquos post-hoc test was used to determine if there were differences between seasons in log(x+1) transformed F enigmaticus tube growth data In both cases all model assumptions were met These analyses were done using the statistical software R version 2151

Figure 2 Ficopomatus enigmaticus tubeworms on colloform formations in a stromatolite pool along the south coast of South Africa (a) ventral view (b) dorsal view (c) and operculum (d) of extracted specimen Photographs by NAF Miranda

Non-parametric permutational MANOVA (PERMANOVA Anderson et al 2008) was used to test for differences in the measured environmental variables In this regard a three-way PERMANOVA design tested for differences between pools uninvaded and invaded (UI) by F enigmaticus (fixed term 2 levels) pools (random factor nested in UI 8 levels) and seasons (fixed factor four levels) The resemblance matrix was based on Euclidean distance Statistical significance was tested using 9999 permutations of residuals under a reduced model Distance-based linear modelling (DISTLM Legendre and Anderson 1999 McArdle and Anderson 2001 Anderson et al 2008) was used to perform permuta-tional regression (9999 random permutations) to test for linear relationships between F enigmaticus abundance (response) and the above-mentioned environmental variables (predictors) The response variable (F enigmaticus abundance) was first converted to a Euclidean distance matrix A step-wise selection procedure was used incorporating the corrected Akaike Information Criterion (AICc) (Burnham and Anderson 2002) as the selection criterion to measure the relative goodness of fit for each model The final subset of environmental variables that provided maximum parsimony (according to the AICc criterion) is presented The a priori significance level (α) for all multivariate tests was set at 001

Invasive polychaete in marine stromatolites

261

Figure 3 Rainfall ocean temperature and swell height data collected in the study area (a-c) selected environmental variables (water temperature salinity available potential area for settlement and pool depth) collected from four stromatolite pools invaded by F enigmaticus (red solid line) and four uninvaded pools (blue dashed line) (d-g) monthly F enigmaticus tube growth in invaded pools (h) and number of F enigmaticus individuals (abundance) per invaded pool (i) Data were collected in 2014 and are presented as monthly means (plusmn SD)

Results

The highest mean TSS and POM values were recorded during summer (supplementary material Table S1) The lowest mean TSS was recorded during spring The lowest mean POM highest mean turbidity and highest mean chl-a were recorded during autumn Temperature was lowest in winter and highest in summer (Table S1 Figure 3) In general all pools were colder and saltier in autumn and winter and warmer and fresher in spring and summer Mean DO ranged between 8 and 12 mgl-1 and mean pH was approximately 8 in all pools While both invaded and uninvaded pools had areas potentially available for settlement throughout the year (Table S1 Figure 3) these were significantly smaller only in uninvaded pools during winter

The density of F enigmaticus was greatest in spring reaching mean (plusmn SE) values of 146 plusmn 130 indm-2

(Table S1) During summer the average increase in tube length reached 686 mm per 30 days (Figure 3) However there were no significant differences in tube growth between seasons (ANOVA P gt 005) Individuals had an average dry mass of 023 plusmn 004 mg tube length of 2145 plusmn 216 mm and reached a biomass of up to 9435 mg dry mass per invaded pool (or 2359 mg m-2) After a mass-mortality event at the end of January 2014 (coinciding with a red tide in the Algoa Bay area and the lowest DO readings recorded in the study) no live F enigmaticus individuals were recorded in 3 of the invaded pools (site C additional pool site B upper and additional pool) from February to August However a few large individuals (average biomass 075 plusmn 002 mg and tube length 2786 plusmn 047 mm) persisted in a single pool (middle pool site B) during autumn and winter (total dry mass 747 mg or 062 mgm-2)

NAF Miranda et al

262

Table 2 PERMANOVA test for differences in abiotic variables across F enigmaticus invaded and uninvaded stromatolite pools (IU fixed factor) pools (random factor nested in IU) and seasons (fixed factor) The degrees of freedom df sum of squares SS means squared MS pseudo ndash F statistic and probability level based on 9999 random permutations P(perm) are presented Significant factors are in bold (α = 001) Data were collected in Eastern Cape stromatolite pools in 2014

Source df SS MS Pseudo-F P(perm)

IU 1 39382 394 0606 0778

Seasons 3 22744 758 8440 0001

Pools (IU) 6 39007 650 8488 0001

IU times Seasons 3 21214 71 0787 0754

Pools(IU) times Seasons 18 16169 90 1173 0093

Residuals 64 4902 77 0606 0778

Total 95 1330

Table 3 Distance-based linear regression model of F enigmaticus abundance (response) against environmental variables (predictors) measured in Eastern Cape stromatolite pools in 2014 (A) Sequential tests for stepwise model (R2 = 026) and percentage of multivariate variation explained by individual axes are presented (B) The most parsimonious model included number of potential substrates for settlement ldquoSubstratesrdquo stromatolite pool water temperature ldquoTemprdquo and available potential area for settlement ldquoAreardquo

A Model summary

Variable AICc SS (trace) Pseudo - F P Prop Cumul res df

Substrates 62640 78690 1180 lt 001 0111 0111 94

Temp (degC) 62095 47619 764 lt 001 0068 0179 93

Area (m2) 61357 54886 963 lt 001 0078 0257 92 B Variation explained by axes

Axis Individual Cumulative Individual Cumulative

explained variation of fitted model explained variation of total variation

1 9821 9821 2521 2521

2 179 100 046 2567

Mean ocean surface temperature was lowest in spring and highest in summer (January and February) (Figure 3) Mean swell height increased in autumn and peaked in winter with this peak coinciding with an increase in mean salinity recorded in all pools in winter while the highest salinities were recorded in invaded pools (Table S1 Figure 3) There was a clear recruitment event at the onset of spring (AugustSeptember) during which 95 plusmn 49 individuals were recorded per invaded pool (Table S1 Figure 3) This coincided with an increase in mean rainfall (gt 50 mm) and a drop in mean swell height at the end of winter (mean swell height remained at approximately 3 m from August to December)

Significant differences in stromatolite pool abiotic data were detected between seasons and pools (Table 2) No significant differences in abiotic conditions were detected however between invaded and uninvaded pools There were differences among seasons and F enigmaticus presence was greater in spring when temperature TSS and POM were higher in the pools

while swell height was lower and ocean temperature was higher in the study area (Figure 4) The stepwise AICc analysis showed that F enigmaticus abundance exhibited a significant relationship with pool tempera-ture number of substrates and area potentially available for settlement (Table 3) However this three variable model only explained 26 of the total variation in F enigmaticus abundance data

Discussion

Ficopomatus enigmaticus is not an obligate reef builder (Bianchi and Morri 2001) and occurs indivi-dually or in small aggregations in the South African stromatolite pools often attached to rocks directly on stromatolites (Figure 2) or on any other available substrates Availability of settlement substrates and water temperature appear to be the most important variables controlling the persistence of F enigmaticus in stromatolite pools Overall environmental variables explained a low percentage of the variation in F enigmaticus abundance (Table 3) This is expected

Invasive polychaete in marine stromatolites

263

for a habitat generalist with wide environmental tolerance However Schwindt et al (2004a) argued that habitats favoured by F enigmaticus populations are very similar in their physical chemical and biological characteristics throughout the world These authors also suggested that the most important variables that affect the spread of this species in invaded habitats may be salinity nutrients (ie TSS POM and chl-a) and environmental energy (eg current speed or swell height as proxy) The TSS POM and chl-a values measured in the current study correspond with the lowest recorded by Schwindt et al (2004a) and therefore may partially explain the relatively small population size observed in stromatolite pools

The use of estuaries and intermittent water bodies as stepping stones for aquatic organisms is well-documented (Burridge et al 2004 Reynolds et al 2014 Tulbure et al 2014) These environments facilitate spread recruitment and invasion of organisms by providing food (OrsquoSullivan et al 2014) a favourable environment during a shift or an unfavourable time period (Hannah et al 2014) and reducing the distance between suitable habitats for organisms with a mobile life stage (Gaines and Bertness 1992) Perhaps not all these factors are necessary For example habitats with unstable environmental characteristics such as stromatolite pools still appear to create suitable stepping stones for habitat generalists such as the estuarine tubeworm

Ficopomatus enigmaticus exhibits gregarious larval settlement which is strongly affected by the ability of the larvae to recognise adults of their own species (Bianchi and Morri 1996) the nature of the settlement substrate and water flow velocity (Kupriyanova et al 2001) Due to their position and physical structure stromatolite pools maintain relatively constant water levels throughout the year and appear to provide a degree of shelter against strong currents that would disrupt larval settlement In agreement with Thorp (1994) the shallow depth of invaded pools led to the development of elevated temperatures during the reproductive period of F enigmaticus within the stromatolites thereby enhancing larval and adult growth Indeed invaded pools may reach higher temperatures than uninvaded pools and the ocean during which time worm growth could escalate Furthermore when over 95 of the population died in invaded pools in February 2014 a small portion of the population survived and persisted during the entire study period in certain stromatolite pools which acted as refuges for F enigmaticus The cause of the demise of F enigmaticus in February is not certain but was possibly linked to a harmful algal bloom prevailing in the area at that time Red tides can cause hypoxic

Figure 4 PCA showing differences in abiotic data collected during 2014 from four invaded and four uninvaded stromatolite pools The PCA is presented with labels for the different seasons (a) and presenceabsence of F enigmaticus (b) The first two axes explain 374 of the total variance (PC1 = 22 and PC2 = 154)

conditions that would have been lethal to F enigma-ticus even though it is tolerant to low dissolved oxygen (Dittmann et al 2009)

Despite its wide salinity and temperature tolerance range environmental conditions do influence growth rates of F enigmaticus (Bianchi and Morri 1996) Rates of tube length growth vary widely (reviewed in Dittmann et al 2009) In this study the fastest F enigmaticus growth rates and greatest abundances were recorded in stromatolite pools during a mass recruitment event at the onset of Austral spring However tube growth was also not significantly different between seasons Furthermore the presence of empty tubes in some pools suggests that worms have survived in greater numbers in the past Post-settlement growth of F enigmaticus juveniles is very fast and particularly affected by salinity and

NAF Miranda et al

264

temperature (Dittmann et al 2009 and references therein) Once individuals settle they can grow to maturity lengths of 6ndash10 mm in a few weeks although this may vary regionally However temperatures exceeding 20ordmC and salinities of 10ndash30 appear to be optimal for F enigmaticus growth (Tebble 1953) Ficopomatus enigmaticus is sensitive to reductions in temperature (Kupriyanova et al 2001) and as with most invertebrates embryonic and larval development time increases with decreasing temperatures (Kupriyanova et al 2001) The minimum temperature value for spawning can vary among populations and is reported to range from 10 to 17degC (Dittmann et al 2009) During the current study average temperatures as low as 145degC were recorded in the ocean in spring while invaded stromatolite pools had average temperatures gt 20degC which seem to be more favourable for growth and reproduction

Ficopomatus enigmaticus larvae are passively distributed by water currents (Kupriyanova et al 2001) and the source of the spawning event that resulted in the early spring recruitment in stromatolite pools is uncertain Perhaps the increase in temperature in pools reduction in swell height and steady rainfall created the required conditions for successful spawning The source of the larvae may have been the persisting population of large adult worms in the stromatolite pools Alternatively F enigmaticus could be introduced through shipping and mariculture (Glasby et al 2007) attached to debris coming from adjacent estuaries with larger populations and even attached to large mobile organisms such as turtles and crabs Although only one period of spawning and settlement was observed in the current study more periods are possible since different populations exhibit variability in settlement periods and reproductive activity seems to be timed to fit the preferred local conditions (Dittmann et al 2009)

As suggested by Hill (1967) for the closely related Ficopomatus uschakovi (Pillai 1960) F enigmaticus may have different salinity optima for survival growth and reproduction The implication is that salinity fluctuations may be critical for the successful reproduction and development of Ficopomatus (Tebble 1953) Fluctuations in temperature and salinity may also exclude competitors and predators of F enigmaticus allowing them to recruit Deeper pools are more stable in terms of temperature but may also be harder to colonize due to biotic barriers such as increased algal growth competition and predation Limitations on potential settlement substrates can result in the use of any available surfaces including roots or other decomposing plant material which is not ideal as the worms are bound to be dislodged Dislodging may also happen when

worms settle on brittle stromatolite deposits However they may persist for long enough to attract other worms and spawn High rates of predation by crabs and molluscs combined with increased competition for food and space with other benthic organisms may explain the absence of F enigmaticus in lower pools (excluded from analyses in this study) Although only environmental variables were considered in this study biotic factors are also important and should be addressed in future studies

The filter-feeding ability of F enigmaticus is remarkable as it can affect whole ecosystems by removing large amounts of particulate matter from the water column thus affecting primary production by removing phytoplankton potentially ameliorating eutrophication and decreasing overall turbidity (Davies et al 1989 Bruschetti et al 2008) However the F enigmaticus population densities in stromatolite pools are much lower than those in estuaries and lagoons where they form reefs Based on clearance rate estimates of 859 mlmgminus1 dry mass of worm hminus1 (Davies et al 1989) worms in the current study filtered a maximum of 19 L of water per pool per day Although turbidity TSS POM and chl-a were marginally lower in some invaded pools compared to uninvaded pools it remains inconclusive whether the feeding of F enigmaticus had a significant effect in stromatolite pools

Wasson et al (2001) indicated that F enigmaticus and other invasive species can make use of suitable estuarine habitats as ldquostepping stonesrdquo Interestingly invasive species can be transferred via stepping stone habitats with potentially unfavourable environmental conditions (Apte et al 2000) Land-use changes in the past few decades have resulted in the introduction of more artificial structures in aquatic environments and increased dumping of waste especially buoyant plastic into coastal waters both of which have been linked to global increases in the spread and biomass of F enigmaticus (Schwindt et al 2004b McQuaid and Griffiths 2014) and other invasive aquatic species (Airoldi et al 2015 Mesel et al 2015) According to Saura et al (2013) the capacity of species to exploit stepping stones depends on species-specific life-history traits This study shows that F enigmaticus is capable of using small freshwater seepage areas along the South African coastline Havel et al (2005) and Johnson et al (2008) reported that small reservoirs and dams also can facilitate the spread of invasive species into seemingly isolated habitats Similarly perhaps unique ecosystems such as stromatolite pools which provide suitable settlement surfaces serve as stepping stones for the spread of a variety of organisms along the coast including invasive species

Invasive polychaete in marine stromatolites

265

Acknowledgements

This work was supported by the South African Research Chairs Initiative of the Department of Science and Technology (DST) and National Research Foundation (NRF) of South Africa Any opinion finding and conclusion or recommendation expressed in this document is that of the authors and the NRF does not accept any liability in this regard The authors wish to thank the South African Weather Service for providing climate data Windguru for their swell and wave predictions and the South African Environmental Observation Network (SAEON) for providing hourly underwater temperature data for the inshore environment We are also grateful to the anonymous reviewers and to Ryan Reisinger and Chris Oosthuizen for their constructive input which strengthened the paper

References

Airoldi L Turon X Perkol-Finkel S Rius M (2015) Corridors for aliens but not for natives effects of marine urban sprawl at a regional scale Diversity and Distributions 21 755ndash768 httpdxdoiorg101111ddi12301

Anderson MJ Gorley RN Clarke KR (2008) PERMANOVA+ for PRIMER Guide to software and statistical methods PRIMER-E Plymouth UK

Apte S Holland B Godwin LS Gardner JA (2000) Jumping Ship a stepping stone event mediating transfer of a non-indigenous species via a potentially unsuitable environment Biological Invasions 2 75ndash79 httpdxdoiorg101023A1010024818644

Bax N Williamson A Aguero M Gonzalez E Geeves W (2003) Marine invasive alien species a threat to global biodiversity Emerging Issues in Oceans Coasts and Islands 27 313ndash323 httpdxdoiorg101016s0308-597x(03)00041-1

Bellard C Leroy B Thuiller W Rysman J-F Courchamp F (2016) Major drivers of invasion risks throughout the world Ecosphere 7 e01241 httpdxdoiorg101002ecs21241

Bianchi CN Morri C (2001) The battle is not to the strong serpulid reefs in the lagoon of Orbetello (Tuscany Italy) Estuarine Coastal and Shelf Science 53 215ndash220 httpdxdoiorg101006 ecss20010793

Bianchi CN Morri C (1996) Ficopomatus ldquoReefsrdquo in the Po River Delta (Northern Adriatic) their constructional dynamics biology and influences on the brackish-water biota Marine Ecology 17 51ndash66 httpdxdoiorg101111j1439-04851996tb00489x

Blackburn TM Lockwood JL Cassey P (2015) The influence of numbers on invasion success Molecular Ecology 24 1942ndash1953 httpdxdoiorg101111mec13075

Bosak T Knoll AH Petroff AP (2013) The meaning of stromatolites Annual Review of Earth and Planetary Sciences 41 21ndash44 httpdxdoiorg101146annurev-earth-042711-105327

Bruschetti M Luppi T Fanjul E Rosenthal A Iribarne O (2008) Grazing effect of the invasive reef-forming polychaete Ficopomatus enigmaticus (Fauvel) on phytoplankton biomass in a SW Atlantic coastal lagoon Journal of Experimental Marine Biology and Ecology 354 212ndash219 httpdxdoiorg101016 jjembe200711009

Burnham KP Anderson DR (2002) Model selection and multimodel inference a practical information-theoretical approach 2nd ed Springer-Verlag New York

Burridge CP Hurt AC Farrington LW Coutin PC Austin CM (2004) Stepping stone gene flow in an estuarine-dwelling sparid from south-east Australia Journal of Fish Biology 64 805ndash819 httpdxdoiorg101111j1095-864920040347x

Cooper JAG Smith AM Arnscheidt J (2013) Contemporary stromatolite formation in high intertidal rock pools Giants Causeway Northern Ireland preliminary observations In Conley DC Masselink G Russell PE OHare TJ (eds) Proceedings 12th International Coastal Symposium (Plymouth England) pp 1675ndash1680 httpdxdoiorg102112si65-2831

Davies BR Stuart V de Villiers M (1989) The filtration activity of a serpulid polychaete population Ficopomatus enigmaticus (Fauvel) and its effects on water quality in a coastal marina Estuarine Coastal and Shelf Science 29 613ndash620 httpdxdoiorg 1010160272-7714(89)90014-0

Day JH (1951) The polychaete fauna of South Africa Part I The intertidal and estuarine Polychaeta of Natal and Mozambique Annals of the Natal Museum 12 1ndash67

Day JH (1981) Estuarine ecology with particular reference to southern Africa AA Balkema Publishers Netherlands 441 pp

Dittmann S Rolston A Benger SN Kupriyanova EK (2009) Habitat requirements distribution and colonisation of the tubeworm Ficopomatus enigmaticus in the Lower Lakes and Coorong Report for the South Australian Murray-Darling Basin Natural Resources Management Board Adelaide 99 pp

Forbes M Vogwill R Onton K (2010) A characterisation of the coastal tufa deposits of southndashwest Western Australia Sedimentary Geology 232 52ndash65 httpdxdoiorg101016jsedgeo 201009009

Fornos JJ Forteza V Martinez-Taberner A (1997) Modern poly-chaete reefs in Western Mediterranean lagoons Ficopomatus enigmaticus (Fauvel) in the Albufera of Menorca Balearic Islands Palaeogeography Palaeoclimatology Palaeoecology 128 175ndash186 httpdxdoiorg101016S0031-0182(96)00045-4

Gaines SD Bertness MD (1992) Dispersal of juveniles and variable recruitment in sessile marine species Nature 360 579ndash580 httpdxdoiorg101038360579a0

Gallardo B Clavero M Saacutenchez MI Vilagrave M (2016) Global eco-logical impacts of invasive speices in aquatic ecosystems Global Change Biology 22 151ndash163 httpdxdoiorg101111gcb13004

Glasby T Connell S Holloway M Hewitt C (2007) Nonindigenous biota on artificial structures could habitat creation facilitate biological invasions Marine Biology 151 887ndash895 httpdxdoiorg101007s00227-006-0552-5

Grotzinger JP Knoll AH (1999) Stromatolites in precambrian carbonates evolutionary mileposts or environmental dipsticks Annual Review of Earth and Planetary Sciences 27 313ndash358 httpdxdoiorg101146annurevearth271313

Hannah L Flint L Syphard AD Moritz MA Buckley LB McCullough IM (2014) Fine-grain modeling of species response to climate change holdouts stepping-stones and microrefugia Trends in Ecology and Evolution 29 390ndash397 httpdxdoiorg101016jtree201404006

Havel JE Lee CE Zanden MJV (2005) Do reservoirs facilitate invasions into landscapes BioScience 55 518ndash525 httpdxdoiorg1016410006-3568(2005)055[0518DRFIIL]20CO2

Johnson PTJ Olden JD Zanden MJV (2008) Dam invaders impoundments facilitate biological invasions into freshwaters Frontiers in Ecology and the Environment 6 357ndash363 httpdxdoiorg101890070156

Kupriyanova EK Nishi E ten Hove HA Rzhavsky AV (2001) Life-history patterns in serpulimorph polychaetes ecological and evolutionary perspectives Oceangraphy and Marine Biology an Annual Review 39 1ndash101

Lau JA Schultheis EH (2015) When two invasion hypotheses are better than one New Phytologist 205 958ndash960 httpdxdoiorg 101111nph13260

Legendre P Anderson MJ (1999) Distance-based redundancy analysis testing multi-species responses in multi-factorial ecological experiments Ecological Monographs 69 1ndash24 httpdxdoiorg1018900012-9615(1999)069[0001DBRATM]20CO2

McArdle BH Anderson MJ (2001) Fitting multivariate models to community data a comment on distance-based redundancy analysis Ecology 82 290ndash297 httpdxdoiorg10189000129658(20 01)082[0290FMMTCD]20CO2

McQuaid KA Griffiths CL (2014) Alien reef-building polychaete drives long-term changes in invertebrate biomass and diversity in a small urban estuary Estuarine Coastal and Shelf Science 138 101ndash106 httpdxdoiorg101016jecss201312016

NAF Miranda et al

260

The availability of substrates suitable for colonisation by F enigmaticus was estimated every month Objects larger than 500 cm3 (such as bottles cans tree trunks and other debris) were regarded as substrates on which F enigmaticus could settle (Schwindt and Iribarne 2000 Schwindt et al 2004a) and were counted in each pool Algal mats can cover hard substrates and effectively create a physical barrier to larval settlement (Norkko and Bonsdorff 1996) Therefore to calculate the total (algae-free) area potentially available for the settlement of F enigmaticus during this study the total hard substrate area of each pool was measured and the percentage benthic algal cover was estimated based on photo-quadrats A 12 megapixel digital camera was positioned 15 m over a 1 times 1 m PVC quadrat which was placed on the water surface and aligned according to landmarks The entire water surface of pools was photographed every month in this way

All pools were searched for traces of tubeworms every month The number of live F enigmaticus individuals was counted in each pool and the length of their calcareous tubes was measured with Vernier callipers (to the nearest 001 mm) Tube growth (increase in length mm) was also tracked for each live individual worm found Photographs were used to confirm the identity of individuals as each displayed distinct settlement locations and tube shapes Measurements were repeated every 30 days and used to determine tube length increases of individual worms Average monthly tube growth rate (increase in length) was then calculated for invaded pools To determine dry mass (biomass) worms (5 individuals per pool) were separated from their tubes oven dried (60degC for 48 h) and individually weighed to the nearest 001 mg

Statistical analyses

General linear models (GLM) with quasi-Poisson distribution (season four levels autumn winter spring summer status two levels invaded and uninvaded) were run for each environmental variable (TSS POM chl-a temperature salinity depth pH turbidity dissolved oxygen potential available area for settlement potential substrates for settlement) followed by Tukeyrsquos post-hoc testing to determine if there were significant differences between invaded and uninvaded pools in each season ANOVA followed by Tukeyrsquos post-hoc test was used to determine if there were differences between seasons in log(x+1) transformed F enigmaticus tube growth data In both cases all model assumptions were met These analyses were done using the statistical software R version 2151

Figure 2 Ficopomatus enigmaticus tubeworms on colloform formations in a stromatolite pool along the south coast of South Africa (a) ventral view (b) dorsal view (c) and operculum (d) of extracted specimen Photographs by NAF Miranda

Non-parametric permutational MANOVA (PERMANOVA Anderson et al 2008) was used to test for differences in the measured environmental variables In this regard a three-way PERMANOVA design tested for differences between pools uninvaded and invaded (UI) by F enigmaticus (fixed term 2 levels) pools (random factor nested in UI 8 levels) and seasons (fixed factor four levels) The resemblance matrix was based on Euclidean distance Statistical significance was tested using 9999 permutations of residuals under a reduced model Distance-based linear modelling (DISTLM Legendre and Anderson 1999 McArdle and Anderson 2001 Anderson et al 2008) was used to perform permuta-tional regression (9999 random permutations) to test for linear relationships between F enigmaticus abundance (response) and the above-mentioned environmental variables (predictors) The response variable (F enigmaticus abundance) was first converted to a Euclidean distance matrix A step-wise selection procedure was used incorporating the corrected Akaike Information Criterion (AICc) (Burnham and Anderson 2002) as the selection criterion to measure the relative goodness of fit for each model The final subset of environmental variables that provided maximum parsimony (according to the AICc criterion) is presented The a priori significance level (α) for all multivariate tests was set at 001

Invasive polychaete in marine stromatolites

261

Figure 3 Rainfall ocean temperature and swell height data collected in the study area (a-c) selected environmental variables (water temperature salinity available potential area for settlement and pool depth) collected from four stromatolite pools invaded by F enigmaticus (red solid line) and four uninvaded pools (blue dashed line) (d-g) monthly F enigmaticus tube growth in invaded pools (h) and number of F enigmaticus individuals (abundance) per invaded pool (i) Data were collected in 2014 and are presented as monthly means (plusmn SD)

Results

The highest mean TSS and POM values were recorded during summer (supplementary material Table S1) The lowest mean TSS was recorded during spring The lowest mean POM highest mean turbidity and highest mean chl-a were recorded during autumn Temperature was lowest in winter and highest in summer (Table S1 Figure 3) In general all pools were colder and saltier in autumn and winter and warmer and fresher in spring and summer Mean DO ranged between 8 and 12 mgl-1 and mean pH was approximately 8 in all pools While both invaded and uninvaded pools had areas potentially available for settlement throughout the year (Table S1 Figure 3) these were significantly smaller only in uninvaded pools during winter

The density of F enigmaticus was greatest in spring reaching mean (plusmn SE) values of 146 plusmn 130 indm-2

(Table S1) During summer the average increase in tube length reached 686 mm per 30 days (Figure 3) However there were no significant differences in tube growth between seasons (ANOVA P gt 005) Individuals had an average dry mass of 023 plusmn 004 mg tube length of 2145 plusmn 216 mm and reached a biomass of up to 9435 mg dry mass per invaded pool (or 2359 mg m-2) After a mass-mortality event at the end of January 2014 (coinciding with a red tide in the Algoa Bay area and the lowest DO readings recorded in the study) no live F enigmaticus individuals were recorded in 3 of the invaded pools (site C additional pool site B upper and additional pool) from February to August However a few large individuals (average biomass 075 plusmn 002 mg and tube length 2786 plusmn 047 mm) persisted in a single pool (middle pool site B) during autumn and winter (total dry mass 747 mg or 062 mgm-2)

NAF Miranda et al

262

Table 2 PERMANOVA test for differences in abiotic variables across F enigmaticus invaded and uninvaded stromatolite pools (IU fixed factor) pools (random factor nested in IU) and seasons (fixed factor) The degrees of freedom df sum of squares SS means squared MS pseudo ndash F statistic and probability level based on 9999 random permutations P(perm) are presented Significant factors are in bold (α = 001) Data were collected in Eastern Cape stromatolite pools in 2014

Source df SS MS Pseudo-F P(perm)

IU 1 39382 394 0606 0778

Seasons 3 22744 758 8440 0001

Pools (IU) 6 39007 650 8488 0001

IU times Seasons 3 21214 71 0787 0754

Pools(IU) times Seasons 18 16169 90 1173 0093

Residuals 64 4902 77 0606 0778

Total 95 1330

Table 3 Distance-based linear regression model of F enigmaticus abundance (response) against environmental variables (predictors) measured in Eastern Cape stromatolite pools in 2014 (A) Sequential tests for stepwise model (R2 = 026) and percentage of multivariate variation explained by individual axes are presented (B) The most parsimonious model included number of potential substrates for settlement ldquoSubstratesrdquo stromatolite pool water temperature ldquoTemprdquo and available potential area for settlement ldquoAreardquo

A Model summary

Variable AICc SS (trace) Pseudo - F P Prop Cumul res df

Substrates 62640 78690 1180 lt 001 0111 0111 94

Temp (degC) 62095 47619 764 lt 001 0068 0179 93

Area (m2) 61357 54886 963 lt 001 0078 0257 92 B Variation explained by axes

Axis Individual Cumulative Individual Cumulative

explained variation of fitted model explained variation of total variation

1 9821 9821 2521 2521

2 179 100 046 2567

Mean ocean surface temperature was lowest in spring and highest in summer (January and February) (Figure 3) Mean swell height increased in autumn and peaked in winter with this peak coinciding with an increase in mean salinity recorded in all pools in winter while the highest salinities were recorded in invaded pools (Table S1 Figure 3) There was a clear recruitment event at the onset of spring (AugustSeptember) during which 95 plusmn 49 individuals were recorded per invaded pool (Table S1 Figure 3) This coincided with an increase in mean rainfall (gt 50 mm) and a drop in mean swell height at the end of winter (mean swell height remained at approximately 3 m from August to December)

Significant differences in stromatolite pool abiotic data were detected between seasons and pools (Table 2) No significant differences in abiotic conditions were detected however between invaded and uninvaded pools There were differences among seasons and F enigmaticus presence was greater in spring when temperature TSS and POM were higher in the pools

while swell height was lower and ocean temperature was higher in the study area (Figure 4) The stepwise AICc analysis showed that F enigmaticus abundance exhibited a significant relationship with pool tempera-ture number of substrates and area potentially available for settlement (Table 3) However this three variable model only explained 26 of the total variation in F enigmaticus abundance data

Discussion

Ficopomatus enigmaticus is not an obligate reef builder (Bianchi and Morri 2001) and occurs indivi-dually or in small aggregations in the South African stromatolite pools often attached to rocks directly on stromatolites (Figure 2) or on any other available substrates Availability of settlement substrates and water temperature appear to be the most important variables controlling the persistence of F enigmaticus in stromatolite pools Overall environmental variables explained a low percentage of the variation in F enigmaticus abundance (Table 3) This is expected

Invasive polychaete in marine stromatolites

263

for a habitat generalist with wide environmental tolerance However Schwindt et al (2004a) argued that habitats favoured by F enigmaticus populations are very similar in their physical chemical and biological characteristics throughout the world These authors also suggested that the most important variables that affect the spread of this species in invaded habitats may be salinity nutrients (ie TSS POM and chl-a) and environmental energy (eg current speed or swell height as proxy) The TSS POM and chl-a values measured in the current study correspond with the lowest recorded by Schwindt et al (2004a) and therefore may partially explain the relatively small population size observed in stromatolite pools

The use of estuaries and intermittent water bodies as stepping stones for aquatic organisms is well-documented (Burridge et al 2004 Reynolds et al 2014 Tulbure et al 2014) These environments facilitate spread recruitment and invasion of organisms by providing food (OrsquoSullivan et al 2014) a favourable environment during a shift or an unfavourable time period (Hannah et al 2014) and reducing the distance between suitable habitats for organisms with a mobile life stage (Gaines and Bertness 1992) Perhaps not all these factors are necessary For example habitats with unstable environmental characteristics such as stromatolite pools still appear to create suitable stepping stones for habitat generalists such as the estuarine tubeworm

Ficopomatus enigmaticus exhibits gregarious larval settlement which is strongly affected by the ability of the larvae to recognise adults of their own species (Bianchi and Morri 1996) the nature of the settlement substrate and water flow velocity (Kupriyanova et al 2001) Due to their position and physical structure stromatolite pools maintain relatively constant water levels throughout the year and appear to provide a degree of shelter against strong currents that would disrupt larval settlement In agreement with Thorp (1994) the shallow depth of invaded pools led to the development of elevated temperatures during the reproductive period of F enigmaticus within the stromatolites thereby enhancing larval and adult growth Indeed invaded pools may reach higher temperatures than uninvaded pools and the ocean during which time worm growth could escalate Furthermore when over 95 of the population died in invaded pools in February 2014 a small portion of the population survived and persisted during the entire study period in certain stromatolite pools which acted as refuges for F enigmaticus The cause of the demise of F enigmaticus in February is not certain but was possibly linked to a harmful algal bloom prevailing in the area at that time Red tides can cause hypoxic

Figure 4 PCA showing differences in abiotic data collected during 2014 from four invaded and four uninvaded stromatolite pools The PCA is presented with labels for the different seasons (a) and presenceabsence of F enigmaticus (b) The first two axes explain 374 of the total variance (PC1 = 22 and PC2 = 154)

conditions that would have been lethal to F enigma-ticus even though it is tolerant to low dissolved oxygen (Dittmann et al 2009)

Despite its wide salinity and temperature tolerance range environmental conditions do influence growth rates of F enigmaticus (Bianchi and Morri 1996) Rates of tube length growth vary widely (reviewed in Dittmann et al 2009) In this study the fastest F enigmaticus growth rates and greatest abundances were recorded in stromatolite pools during a mass recruitment event at the onset of Austral spring However tube growth was also not significantly different between seasons Furthermore the presence of empty tubes in some pools suggests that worms have survived in greater numbers in the past Post-settlement growth of F enigmaticus juveniles is very fast and particularly affected by salinity and

NAF Miranda et al

264

temperature (Dittmann et al 2009 and references therein) Once individuals settle they can grow to maturity lengths of 6ndash10 mm in a few weeks although this may vary regionally However temperatures exceeding 20ordmC and salinities of 10ndash30 appear to be optimal for F enigmaticus growth (Tebble 1953) Ficopomatus enigmaticus is sensitive to reductions in temperature (Kupriyanova et al 2001) and as with most invertebrates embryonic and larval development time increases with decreasing temperatures (Kupriyanova et al 2001) The minimum temperature value for spawning can vary among populations and is reported to range from 10 to 17degC (Dittmann et al 2009) During the current study average temperatures as low as 145degC were recorded in the ocean in spring while invaded stromatolite pools had average temperatures gt 20degC which seem to be more favourable for growth and reproduction

Ficopomatus enigmaticus larvae are passively distributed by water currents (Kupriyanova et al 2001) and the source of the spawning event that resulted in the early spring recruitment in stromatolite pools is uncertain Perhaps the increase in temperature in pools reduction in swell height and steady rainfall created the required conditions for successful spawning The source of the larvae may have been the persisting population of large adult worms in the stromatolite pools Alternatively F enigmaticus could be introduced through shipping and mariculture (Glasby et al 2007) attached to debris coming from adjacent estuaries with larger populations and even attached to large mobile organisms such as turtles and crabs Although only one period of spawning and settlement was observed in the current study more periods are possible since different populations exhibit variability in settlement periods and reproductive activity seems to be timed to fit the preferred local conditions (Dittmann et al 2009)

As suggested by Hill (1967) for the closely related Ficopomatus uschakovi (Pillai 1960) F enigmaticus may have different salinity optima for survival growth and reproduction The implication is that salinity fluctuations may be critical for the successful reproduction and development of Ficopomatus (Tebble 1953) Fluctuations in temperature and salinity may also exclude competitors and predators of F enigmaticus allowing them to recruit Deeper pools are more stable in terms of temperature but may also be harder to colonize due to biotic barriers such as increased algal growth competition and predation Limitations on potential settlement substrates can result in the use of any available surfaces including roots or other decomposing plant material which is not ideal as the worms are bound to be dislodged Dislodging may also happen when

worms settle on brittle stromatolite deposits However they may persist for long enough to attract other worms and spawn High rates of predation by crabs and molluscs combined with increased competition for food and space with other benthic organisms may explain the absence of F enigmaticus in lower pools (excluded from analyses in this study) Although only environmental variables were considered in this study biotic factors are also important and should be addressed in future studies

The filter-feeding ability of F enigmaticus is remarkable as it can affect whole ecosystems by removing large amounts of particulate matter from the water column thus affecting primary production by removing phytoplankton potentially ameliorating eutrophication and decreasing overall turbidity (Davies et al 1989 Bruschetti et al 2008) However the F enigmaticus population densities in stromatolite pools are much lower than those in estuaries and lagoons where they form reefs Based on clearance rate estimates of 859 mlmgminus1 dry mass of worm hminus1 (Davies et al 1989) worms in the current study filtered a maximum of 19 L of water per pool per day Although turbidity TSS POM and chl-a were marginally lower in some invaded pools compared to uninvaded pools it remains inconclusive whether the feeding of F enigmaticus had a significant effect in stromatolite pools

Wasson et al (2001) indicated that F enigmaticus and other invasive species can make use of suitable estuarine habitats as ldquostepping stonesrdquo Interestingly invasive species can be transferred via stepping stone habitats with potentially unfavourable environmental conditions (Apte et al 2000) Land-use changes in the past few decades have resulted in the introduction of more artificial structures in aquatic environments and increased dumping of waste especially buoyant plastic into coastal waters both of which have been linked to global increases in the spread and biomass of F enigmaticus (Schwindt et al 2004b McQuaid and Griffiths 2014) and other invasive aquatic species (Airoldi et al 2015 Mesel et al 2015) According to Saura et al (2013) the capacity of species to exploit stepping stones depends on species-specific life-history traits This study shows that F enigmaticus is capable of using small freshwater seepage areas along the South African coastline Havel et al (2005) and Johnson et al (2008) reported that small reservoirs and dams also can facilitate the spread of invasive species into seemingly isolated habitats Similarly perhaps unique ecosystems such as stromatolite pools which provide suitable settlement surfaces serve as stepping stones for the spread of a variety of organisms along the coast including invasive species

Invasive polychaete in marine stromatolites

265

Acknowledgements

This work was supported by the South African Research Chairs Initiative of the Department of Science and Technology (DST) and National Research Foundation (NRF) of South Africa Any opinion finding and conclusion or recommendation expressed in this document is that of the authors and the NRF does not accept any liability in this regard The authors wish to thank the South African Weather Service for providing climate data Windguru for their swell and wave predictions and the South African Environmental Observation Network (SAEON) for providing hourly underwater temperature data for the inshore environment We are also grateful to the anonymous reviewers and to Ryan Reisinger and Chris Oosthuizen for their constructive input which strengthened the paper

References

Airoldi L Turon X Perkol-Finkel S Rius M (2015) Corridors for aliens but not for natives effects of marine urban sprawl at a regional scale Diversity and Distributions 21 755ndash768 httpdxdoiorg101111ddi12301

Anderson MJ Gorley RN Clarke KR (2008) PERMANOVA+ for PRIMER Guide to software and statistical methods PRIMER-E Plymouth UK

Apte S Holland B Godwin LS Gardner JA (2000) Jumping Ship a stepping stone event mediating transfer of a non-indigenous species via a potentially unsuitable environment Biological Invasions 2 75ndash79 httpdxdoiorg101023A1010024818644

Bax N Williamson A Aguero M Gonzalez E Geeves W (2003) Marine invasive alien species a threat to global biodiversity Emerging Issues in Oceans Coasts and Islands 27 313ndash323 httpdxdoiorg101016s0308-597x(03)00041-1

Bellard C Leroy B Thuiller W Rysman J-F Courchamp F (2016) Major drivers of invasion risks throughout the world Ecosphere 7 e01241 httpdxdoiorg101002ecs21241

Bianchi CN Morri C (2001) The battle is not to the strong serpulid reefs in the lagoon of Orbetello (Tuscany Italy) Estuarine Coastal and Shelf Science 53 215ndash220 httpdxdoiorg101006 ecss20010793

Bianchi CN Morri C (1996) Ficopomatus ldquoReefsrdquo in the Po River Delta (Northern Adriatic) their constructional dynamics biology and influences on the brackish-water biota Marine Ecology 17 51ndash66 httpdxdoiorg101111j1439-04851996tb00489x

Blackburn TM Lockwood JL Cassey P (2015) The influence of numbers on invasion success Molecular Ecology 24 1942ndash1953 httpdxdoiorg101111mec13075

Bosak T Knoll AH Petroff AP (2013) The meaning of stromatolites Annual Review of Earth and Planetary Sciences 41 21ndash44 httpdxdoiorg101146annurev-earth-042711-105327

Bruschetti M Luppi T Fanjul E Rosenthal A Iribarne O (2008) Grazing effect of the invasive reef-forming polychaete Ficopomatus enigmaticus (Fauvel) on phytoplankton biomass in a SW Atlantic coastal lagoon Journal of Experimental Marine Biology and Ecology 354 212ndash219 httpdxdoiorg101016 jjembe200711009

Burnham KP Anderson DR (2002) Model selection and multimodel inference a practical information-theoretical approach 2nd ed Springer-Verlag New York

Burridge CP Hurt AC Farrington LW Coutin PC Austin CM (2004) Stepping stone gene flow in an estuarine-dwelling sparid from south-east Australia Journal of Fish Biology 64 805ndash819 httpdxdoiorg101111j1095-864920040347x

Cooper JAG Smith AM Arnscheidt J (2013) Contemporary stromatolite formation in high intertidal rock pools Giants Causeway Northern Ireland preliminary observations In Conley DC Masselink G Russell PE OHare TJ (eds) Proceedings 12th International Coastal Symposium (Plymouth England) pp 1675ndash1680 httpdxdoiorg102112si65-2831

Davies BR Stuart V de Villiers M (1989) The filtration activity of a serpulid polychaete population Ficopomatus enigmaticus (Fauvel) and its effects on water quality in a coastal marina Estuarine Coastal and Shelf Science 29 613ndash620 httpdxdoiorg 1010160272-7714(89)90014-0

Day JH (1951) The polychaete fauna of South Africa Part I The intertidal and estuarine Polychaeta of Natal and Mozambique Annals of the Natal Museum 12 1ndash67

Day JH (1981) Estuarine ecology with particular reference to southern Africa AA Balkema Publishers Netherlands 441 pp

Dittmann S Rolston A Benger SN Kupriyanova EK (2009) Habitat requirements distribution and colonisation of the tubeworm Ficopomatus enigmaticus in the Lower Lakes and Coorong Report for the South Australian Murray-Darling Basin Natural Resources Management Board Adelaide 99 pp

Forbes M Vogwill R Onton K (2010) A characterisation of the coastal tufa deposits of southndashwest Western Australia Sedimentary Geology 232 52ndash65 httpdxdoiorg101016jsedgeo 201009009

Fornos JJ Forteza V Martinez-Taberner A (1997) Modern poly-chaete reefs in Western Mediterranean lagoons Ficopomatus enigmaticus (Fauvel) in the Albufera of Menorca Balearic Islands Palaeogeography Palaeoclimatology Palaeoecology 128 175ndash186 httpdxdoiorg101016S0031-0182(96)00045-4

Gaines SD Bertness MD (1992) Dispersal of juveniles and variable recruitment in sessile marine species Nature 360 579ndash580 httpdxdoiorg101038360579a0

Gallardo B Clavero M Saacutenchez MI Vilagrave M (2016) Global eco-logical impacts of invasive speices in aquatic ecosystems Global Change Biology 22 151ndash163 httpdxdoiorg101111gcb13004

Glasby T Connell S Holloway M Hewitt C (2007) Nonindigenous biota on artificial structures could habitat creation facilitate biological invasions Marine Biology 151 887ndash895 httpdxdoiorg101007s00227-006-0552-5

Grotzinger JP Knoll AH (1999) Stromatolites in precambrian carbonates evolutionary mileposts or environmental dipsticks Annual Review of Earth and Planetary Sciences 27 313ndash358 httpdxdoiorg101146annurevearth271313

Hannah L Flint L Syphard AD Moritz MA Buckley LB McCullough IM (2014) Fine-grain modeling of species response to climate change holdouts stepping-stones and microrefugia Trends in Ecology and Evolution 29 390ndash397 httpdxdoiorg101016jtree201404006

Havel JE Lee CE Zanden MJV (2005) Do reservoirs facilitate invasions into landscapes BioScience 55 518ndash525 httpdxdoiorg1016410006-3568(2005)055[0518DRFIIL]20CO2

Johnson PTJ Olden JD Zanden MJV (2008) Dam invaders impoundments facilitate biological invasions into freshwaters Frontiers in Ecology and the Environment 6 357ndash363 httpdxdoiorg101890070156

Kupriyanova EK Nishi E ten Hove HA Rzhavsky AV (2001) Life-history patterns in serpulimorph polychaetes ecological and evolutionary perspectives Oceangraphy and Marine Biology an Annual Review 39 1ndash101

Lau JA Schultheis EH (2015) When two invasion hypotheses are better than one New Phytologist 205 958ndash960 httpdxdoiorg 101111nph13260

Legendre P Anderson MJ (1999) Distance-based redundancy analysis testing multi-species responses in multi-factorial ecological experiments Ecological Monographs 69 1ndash24 httpdxdoiorg1018900012-9615(1999)069[0001DBRATM]20CO2

McArdle BH Anderson MJ (2001) Fitting multivariate models to community data a comment on distance-based redundancy analysis Ecology 82 290ndash297 httpdxdoiorg10189000129658(20 01)082[0290FMMTCD]20CO2

McQuaid KA Griffiths CL (2014) Alien reef-building polychaete drives long-term changes in invertebrate biomass and diversity in a small urban estuary Estuarine Coastal and Shelf Science 138 101ndash106 httpdxdoiorg101016jecss201312016

Invasive polychaete in marine stromatolites

261

Figure 3 Rainfall ocean temperature and swell height data collected in the study area (a-c) selected environmental variables (water temperature salinity available potential area for settlement and pool depth) collected from four stromatolite pools invaded by F enigmaticus (red solid line) and four uninvaded pools (blue dashed line) (d-g) monthly F enigmaticus tube growth in invaded pools (h) and number of F enigmaticus individuals (abundance) per invaded pool (i) Data were collected in 2014 and are presented as monthly means (plusmn SD)

Results

The highest mean TSS and POM values were recorded during summer (supplementary material Table S1) The lowest mean TSS was recorded during spring The lowest mean POM highest mean turbidity and highest mean chl-a were recorded during autumn Temperature was lowest in winter and highest in summer (Table S1 Figure 3) In general all pools were colder and saltier in autumn and winter and warmer and fresher in spring and summer Mean DO ranged between 8 and 12 mgl-1 and mean pH was approximately 8 in all pools While both invaded and uninvaded pools had areas potentially available for settlement throughout the year (Table S1 Figure 3) these were significantly smaller only in uninvaded pools during winter

The density of F enigmaticus was greatest in spring reaching mean (plusmn SE) values of 146 plusmn 130 indm-2

(Table S1) During summer the average increase in tube length reached 686 mm per 30 days (Figure 3) However there were no significant differences in tube growth between seasons (ANOVA P gt 005) Individuals had an average dry mass of 023 plusmn 004 mg tube length of 2145 plusmn 216 mm and reached a biomass of up to 9435 mg dry mass per invaded pool (or 2359 mg m-2) After a mass-mortality event at the end of January 2014 (coinciding with a red tide in the Algoa Bay area and the lowest DO readings recorded in the study) no live F enigmaticus individuals were recorded in 3 of the invaded pools (site C additional pool site B upper and additional pool) from February to August However a few large individuals (average biomass 075 plusmn 002 mg and tube length 2786 plusmn 047 mm) persisted in a single pool (middle pool site B) during autumn and winter (total dry mass 747 mg or 062 mgm-2)

NAF Miranda et al

262

Table 2 PERMANOVA test for differences in abiotic variables across F enigmaticus invaded and uninvaded stromatolite pools (IU fixed factor) pools (random factor nested in IU) and seasons (fixed factor) The degrees of freedom df sum of squares SS means squared MS pseudo ndash F statistic and probability level based on 9999 random permutations P(perm) are presented Significant factors are in bold (α = 001) Data were collected in Eastern Cape stromatolite pools in 2014

Source df SS MS Pseudo-F P(perm)

IU 1 39382 394 0606 0778

Seasons 3 22744 758 8440 0001

Pools (IU) 6 39007 650 8488 0001

IU times Seasons 3 21214 71 0787 0754

Pools(IU) times Seasons 18 16169 90 1173 0093

Residuals 64 4902 77 0606 0778

Total 95 1330

Table 3 Distance-based linear regression model of F enigmaticus abundance (response) against environmental variables (predictors) measured in Eastern Cape stromatolite pools in 2014 (A) Sequential tests for stepwise model (R2 = 026) and percentage of multivariate variation explained by individual axes are presented (B) The most parsimonious model included number of potential substrates for settlement ldquoSubstratesrdquo stromatolite pool water temperature ldquoTemprdquo and available potential area for settlement ldquoAreardquo

A Model summary

Variable AICc SS (trace) Pseudo - F P Prop Cumul res df

Substrates 62640 78690 1180 lt 001 0111 0111 94

Temp (degC) 62095 47619 764 lt 001 0068 0179 93

Area (m2) 61357 54886 963 lt 001 0078 0257 92 B Variation explained by axes

Axis Individual Cumulative Individual Cumulative

explained variation of fitted model explained variation of total variation

1 9821 9821 2521 2521

2 179 100 046 2567

Mean ocean surface temperature was lowest in spring and highest in summer (January and February) (Figure 3) Mean swell height increased in autumn and peaked in winter with this peak coinciding with an increase in mean salinity recorded in all pools in winter while the highest salinities were recorded in invaded pools (Table S1 Figure 3) There was a clear recruitment event at the onset of spring (AugustSeptember) during which 95 plusmn 49 individuals were recorded per invaded pool (Table S1 Figure 3) This coincided with an increase in mean rainfall (gt 50 mm) and a drop in mean swell height at the end of winter (mean swell height remained at approximately 3 m from August to December)

Significant differences in stromatolite pool abiotic data were detected between seasons and pools (Table 2) No significant differences in abiotic conditions were detected however between invaded and uninvaded pools There were differences among seasons and F enigmaticus presence was greater in spring when temperature TSS and POM were higher in the pools

while swell height was lower and ocean temperature was higher in the study area (Figure 4) The stepwise AICc analysis showed that F enigmaticus abundance exhibited a significant relationship with pool tempera-ture number of substrates and area potentially available for settlement (Table 3) However this three variable model only explained 26 of the total variation in F enigmaticus abundance data

Discussion

Ficopomatus enigmaticus is not an obligate reef builder (Bianchi and Morri 2001) and occurs indivi-dually or in small aggregations in the South African stromatolite pools often attached to rocks directly on stromatolites (Figure 2) or on any other available substrates Availability of settlement substrates and water temperature appear to be the most important variables controlling the persistence of F enigmaticus in stromatolite pools Overall environmental variables explained a low percentage of the variation in F enigmaticus abundance (Table 3) This is expected

Invasive polychaete in marine stromatolites

263

for a habitat generalist with wide environmental tolerance However Schwindt et al (2004a) argued that habitats favoured by F enigmaticus populations are very similar in their physical chemical and biological characteristics throughout the world These authors also suggested that the most important variables that affect the spread of this species in invaded habitats may be salinity nutrients (ie TSS POM and chl-a) and environmental energy (eg current speed or swell height as proxy) The TSS POM and chl-a values measured in the current study correspond with the lowest recorded by Schwindt et al (2004a) and therefore may partially explain the relatively small population size observed in stromatolite pools

The use of estuaries and intermittent water bodies as stepping stones for aquatic organisms is well-documented (Burridge et al 2004 Reynolds et al 2014 Tulbure et al 2014) These environments facilitate spread recruitment and invasion of organisms by providing food (OrsquoSullivan et al 2014) a favourable environment during a shift or an unfavourable time period (Hannah et al 2014) and reducing the distance between suitable habitats for organisms with a mobile life stage (Gaines and Bertness 1992) Perhaps not all these factors are necessary For example habitats with unstable environmental characteristics such as stromatolite pools still appear to create suitable stepping stones for habitat generalists such as the estuarine tubeworm

Ficopomatus enigmaticus exhibits gregarious larval settlement which is strongly affected by the ability of the larvae to recognise adults of their own species (Bianchi and Morri 1996) the nature of the settlement substrate and water flow velocity (Kupriyanova et al 2001) Due to their position and physical structure stromatolite pools maintain relatively constant water levels throughout the year and appear to provide a degree of shelter against strong currents that would disrupt larval settlement In agreement with Thorp (1994) the shallow depth of invaded pools led to the development of elevated temperatures during the reproductive period of F enigmaticus within the stromatolites thereby enhancing larval and adult growth Indeed invaded pools may reach higher temperatures than uninvaded pools and the ocean during which time worm growth could escalate Furthermore when over 95 of the population died in invaded pools in February 2014 a small portion of the population survived and persisted during the entire study period in certain stromatolite pools which acted as refuges for F enigmaticus The cause of the demise of F enigmaticus in February is not certain but was possibly linked to a harmful algal bloom prevailing in the area at that time Red tides can cause hypoxic

Figure 4 PCA showing differences in abiotic data collected during 2014 from four invaded and four uninvaded stromatolite pools The PCA is presented with labels for the different seasons (a) and presenceabsence of F enigmaticus (b) The first two axes explain 374 of the total variance (PC1 = 22 and PC2 = 154)

conditions that would have been lethal to F enigma-ticus even though it is tolerant to low dissolved oxygen (Dittmann et al 2009)

Despite its wide salinity and temperature tolerance range environmental conditions do influence growth rates of F enigmaticus (Bianchi and Morri 1996) Rates of tube length growth vary widely (reviewed in Dittmann et al 2009) In this study the fastest F enigmaticus growth rates and greatest abundances were recorded in stromatolite pools during a mass recruitment event at the onset of Austral spring However tube growth was also not significantly different between seasons Furthermore the presence of empty tubes in some pools suggests that worms have survived in greater numbers in the past Post-settlement growth of F enigmaticus juveniles is very fast and particularly affected by salinity and

NAF Miranda et al

264

temperature (Dittmann et al 2009 and references therein) Once individuals settle they can grow to maturity lengths of 6ndash10 mm in a few weeks although this may vary regionally However temperatures exceeding 20ordmC and salinities of 10ndash30 appear to be optimal for F enigmaticus growth (Tebble 1953) Ficopomatus enigmaticus is sensitive to reductions in temperature (Kupriyanova et al 2001) and as with most invertebrates embryonic and larval development time increases with decreasing temperatures (Kupriyanova et al 2001) The minimum temperature value for spawning can vary among populations and is reported to range from 10 to 17degC (Dittmann et al 2009) During the current study average temperatures as low as 145degC were recorded in the ocean in spring while invaded stromatolite pools had average temperatures gt 20degC which seem to be more favourable for growth and reproduction

Ficopomatus enigmaticus larvae are passively distributed by water currents (Kupriyanova et al 2001) and the source of the spawning event that resulted in the early spring recruitment in stromatolite pools is uncertain Perhaps the increase in temperature in pools reduction in swell height and steady rainfall created the required conditions for successful spawning The source of the larvae may have been the persisting population of large adult worms in the stromatolite pools Alternatively F enigmaticus could be introduced through shipping and mariculture (Glasby et al 2007) attached to debris coming from adjacent estuaries with larger populations and even attached to large mobile organisms such as turtles and crabs Although only one period of spawning and settlement was observed in the current study more periods are possible since different populations exhibit variability in settlement periods and reproductive activity seems to be timed to fit the preferred local conditions (Dittmann et al 2009)

As suggested by Hill (1967) for the closely related Ficopomatus uschakovi (Pillai 1960) F enigmaticus may have different salinity optima for survival growth and reproduction The implication is that salinity fluctuations may be critical for the successful reproduction and development of Ficopomatus (Tebble 1953) Fluctuations in temperature and salinity may also exclude competitors and predators of F enigmaticus allowing them to recruit Deeper pools are more stable in terms of temperature but may also be harder to colonize due to biotic barriers such as increased algal growth competition and predation Limitations on potential settlement substrates can result in the use of any available surfaces including roots or other decomposing plant material which is not ideal as the worms are bound to be dislodged Dislodging may also happen when

worms settle on brittle stromatolite deposits However they may persist for long enough to attract other worms and spawn High rates of predation by crabs and molluscs combined with increased competition for food and space with other benthic organisms may explain the absence of F enigmaticus in lower pools (excluded from analyses in this study) Although only environmental variables were considered in this study biotic factors are also important and should be addressed in future studies

The filter-feeding ability of F enigmaticus is remarkable as it can affect whole ecosystems by removing large amounts of particulate matter from the water column thus affecting primary production by removing phytoplankton potentially ameliorating eutrophication and decreasing overall turbidity (Davies et al 1989 Bruschetti et al 2008) However the F enigmaticus population densities in stromatolite pools are much lower than those in estuaries and lagoons where they form reefs Based on clearance rate estimates of 859 mlmgminus1 dry mass of worm hminus1 (Davies et al 1989) worms in the current study filtered a maximum of 19 L of water per pool per day Although turbidity TSS POM and chl-a were marginally lower in some invaded pools compared to uninvaded pools it remains inconclusive whether the feeding of F enigmaticus had a significant effect in stromatolite pools

Wasson et al (2001) indicated that F enigmaticus and other invasive species can make use of suitable estuarine habitats as ldquostepping stonesrdquo Interestingly invasive species can be transferred via stepping stone habitats with potentially unfavourable environmental conditions (Apte et al 2000) Land-use changes in the past few decades have resulted in the introduction of more artificial structures in aquatic environments and increased dumping of waste especially buoyant plastic into coastal waters both of which have been linked to global increases in the spread and biomass of F enigmaticus (Schwindt et al 2004b McQuaid and Griffiths 2014) and other invasive aquatic species (Airoldi et al 2015 Mesel et al 2015) According to Saura et al (2013) the capacity of species to exploit stepping stones depends on species-specific life-history traits This study shows that F enigmaticus is capable of using small freshwater seepage areas along the South African coastline Havel et al (2005) and Johnson et al (2008) reported that small reservoirs and dams also can facilitate the spread of invasive species into seemingly isolated habitats Similarly perhaps unique ecosystems such as stromatolite pools which provide suitable settlement surfaces serve as stepping stones for the spread of a variety of organisms along the coast including invasive species

Invasive polychaete in marine stromatolites

265

Acknowledgements

This work was supported by the South African Research Chairs Initiative of the Department of Science and Technology (DST) and National Research Foundation (NRF) of South Africa Any opinion finding and conclusion or recommendation expressed in this document is that of the authors and the NRF does not accept any liability in this regard The authors wish to thank the South African Weather Service for providing climate data Windguru for their swell and wave predictions and the South African Environmental Observation Network (SAEON) for providing hourly underwater temperature data for the inshore environment We are also grateful to the anonymous reviewers and to Ryan Reisinger and Chris Oosthuizen for their constructive input which strengthened the paper

References

Airoldi L Turon X Perkol-Finkel S Rius M (2015) Corridors for aliens but not for natives effects of marine urban sprawl at a regional scale Diversity and Distributions 21 755ndash768 httpdxdoiorg101111ddi12301

Anderson MJ Gorley RN Clarke KR (2008) PERMANOVA+ for PRIMER Guide to software and statistical methods PRIMER-E Plymouth UK

Apte S Holland B Godwin LS Gardner JA (2000) Jumping Ship a stepping stone event mediating transfer of a non-indigenous species via a potentially unsuitable environment Biological Invasions 2 75ndash79 httpdxdoiorg101023A1010024818644

Bax N Williamson A Aguero M Gonzalez E Geeves W (2003) Marine invasive alien species a threat to global biodiversity Emerging Issues in Oceans Coasts and Islands 27 313ndash323 httpdxdoiorg101016s0308-597x(03)00041-1

Bellard C Leroy B Thuiller W Rysman J-F Courchamp F (2016) Major drivers of invasion risks throughout the world Ecosphere 7 e01241 httpdxdoiorg101002ecs21241

Bianchi CN Morri C (2001) The battle is not to the strong serpulid reefs in the lagoon of Orbetello (Tuscany Italy) Estuarine Coastal and Shelf Science 53 215ndash220 httpdxdoiorg101006 ecss20010793

Bianchi CN Morri C (1996) Ficopomatus ldquoReefsrdquo in the Po River Delta (Northern Adriatic) their constructional dynamics biology and influences on the brackish-water biota Marine Ecology 17 51ndash66 httpdxdoiorg101111j1439-04851996tb00489x

Blackburn TM Lockwood JL Cassey P (2015) The influence of numbers on invasion success Molecular Ecology 24 1942ndash1953 httpdxdoiorg101111mec13075

Bosak T Knoll AH Petroff AP (2013) The meaning of stromatolites Annual Review of Earth and Planetary Sciences 41 21ndash44 httpdxdoiorg101146annurev-earth-042711-105327

Bruschetti M Luppi T Fanjul E Rosenthal A Iribarne O (2008) Grazing effect of the invasive reef-forming polychaete Ficopomatus enigmaticus (Fauvel) on phytoplankton biomass in a SW Atlantic coastal lagoon Journal of Experimental Marine Biology and Ecology 354 212ndash219 httpdxdoiorg101016 jjembe200711009

Burnham KP Anderson DR (2002) Model selection and multimodel inference a practical information-theoretical approach 2nd ed Springer-Verlag New York

Burridge CP Hurt AC Farrington LW Coutin PC Austin CM (2004) Stepping stone gene flow in an estuarine-dwelling sparid from south-east Australia Journal of Fish Biology 64 805ndash819 httpdxdoiorg101111j1095-864920040347x

Cooper JAG Smith AM Arnscheidt J (2013) Contemporary stromatolite formation in high intertidal rock pools Giants Causeway Northern Ireland preliminary observations In Conley DC Masselink G Russell PE OHare TJ (eds) Proceedings 12th International Coastal Symposium (Plymouth England) pp 1675ndash1680 httpdxdoiorg102112si65-2831

Davies BR Stuart V de Villiers M (1989) The filtration activity of a serpulid polychaete population Ficopomatus enigmaticus (Fauvel) and its effects on water quality in a coastal marina Estuarine Coastal and Shelf Science 29 613ndash620 httpdxdoiorg 1010160272-7714(89)90014-0

Day JH (1951) The polychaete fauna of South Africa Part I The intertidal and estuarine Polychaeta of Natal and Mozambique Annals of the Natal Museum 12 1ndash67

Day JH (1981) Estuarine ecology with particular reference to southern Africa AA Balkema Publishers Netherlands 441 pp

Dittmann S Rolston A Benger SN Kupriyanova EK (2009) Habitat requirements distribution and colonisation of the tubeworm Ficopomatus enigmaticus in the Lower Lakes and Coorong Report for the South Australian Murray-Darling Basin Natural Resources Management Board Adelaide 99 pp

Forbes M Vogwill R Onton K (2010) A characterisation of the coastal tufa deposits of southndashwest Western Australia Sedimentary Geology 232 52ndash65 httpdxdoiorg101016jsedgeo 201009009

Fornos JJ Forteza V Martinez-Taberner A (1997) Modern poly-chaete reefs in Western Mediterranean lagoons Ficopomatus enigmaticus (Fauvel) in the Albufera of Menorca Balearic Islands Palaeogeography Palaeoclimatology Palaeoecology 128 175ndash186 httpdxdoiorg101016S0031-0182(96)00045-4

Gaines SD Bertness MD (1992) Dispersal of juveniles and variable recruitment in sessile marine species Nature 360 579ndash580 httpdxdoiorg101038360579a0

Gallardo B Clavero M Saacutenchez MI Vilagrave M (2016) Global eco-logical impacts of invasive speices in aquatic ecosystems Global Change Biology 22 151ndash163 httpdxdoiorg101111gcb13004

Glasby T Connell S Holloway M Hewitt C (2007) Nonindigenous biota on artificial structures could habitat creation facilitate biological invasions Marine Biology 151 887ndash895 httpdxdoiorg101007s00227-006-0552-5

Grotzinger JP Knoll AH (1999) Stromatolites in precambrian carbonates evolutionary mileposts or environmental dipsticks Annual Review of Earth and Planetary Sciences 27 313ndash358 httpdxdoiorg101146annurevearth271313

Hannah L Flint L Syphard AD Moritz MA Buckley LB McCullough IM (2014) Fine-grain modeling of species response to climate change holdouts stepping-stones and microrefugia Trends in Ecology and Evolution 29 390ndash397 httpdxdoiorg101016jtree201404006

Havel JE Lee CE Zanden MJV (2005) Do reservoirs facilitate invasions into landscapes BioScience 55 518ndash525 httpdxdoiorg1016410006-3568(2005)055[0518DRFIIL]20CO2

Johnson PTJ Olden JD Zanden MJV (2008) Dam invaders impoundments facilitate biological invasions into freshwaters Frontiers in Ecology and the Environment 6 357ndash363 httpdxdoiorg101890070156

Kupriyanova EK Nishi E ten Hove HA Rzhavsky AV (2001) Life-history patterns in serpulimorph polychaetes ecological and evolutionary perspectives Oceangraphy and Marine Biology an Annual Review 39 1ndash101

Lau JA Schultheis EH (2015) When two invasion hypotheses are better than one New Phytologist 205 958ndash960 httpdxdoiorg 101111nph13260

Legendre P Anderson MJ (1999) Distance-based redundancy analysis testing multi-species responses in multi-factorial ecological experiments Ecological Monographs 69 1ndash24 httpdxdoiorg1018900012-9615(1999)069[0001DBRATM]20CO2

McArdle BH Anderson MJ (2001) Fitting multivariate models to community data a comment on distance-based redundancy analysis Ecology 82 290ndash297 httpdxdoiorg10189000129658(20 01)082[0290FMMTCD]20CO2

McQuaid KA Griffiths CL (2014) Alien reef-building polychaete drives long-term changes in invertebrate biomass and diversity in a small urban estuary Estuarine Coastal and Shelf Science 138 101ndash106 httpdxdoiorg101016jecss201312016

NAF Miranda et al

262

Table 2 PERMANOVA test for differences in abiotic variables across F enigmaticus invaded and uninvaded stromatolite pools (IU fixed factor) pools (random factor nested in IU) and seasons (fixed factor) The degrees of freedom df sum of squares SS means squared MS pseudo ndash F statistic and probability level based on 9999 random permutations P(perm) are presented Significant factors are in bold (α = 001) Data were collected in Eastern Cape stromatolite pools in 2014

Source df SS MS Pseudo-F P(perm)

IU 1 39382 394 0606 0778

Seasons 3 22744 758 8440 0001

Pools (IU) 6 39007 650 8488 0001

IU times Seasons 3 21214 71 0787 0754

Pools(IU) times Seasons 18 16169 90 1173 0093

Residuals 64 4902 77 0606 0778

Total 95 1330

Table 3 Distance-based linear regression model of F enigmaticus abundance (response) against environmental variables (predictors) measured in Eastern Cape stromatolite pools in 2014 (A) Sequential tests for stepwise model (R2 = 026) and percentage of multivariate variation explained by individual axes are presented (B) The most parsimonious model included number of potential substrates for settlement ldquoSubstratesrdquo stromatolite pool water temperature ldquoTemprdquo and available potential area for settlement ldquoAreardquo

A Model summary

Variable AICc SS (trace) Pseudo - F P Prop Cumul res df

Substrates 62640 78690 1180 lt 001 0111 0111 94

Temp (degC) 62095 47619 764 lt 001 0068 0179 93

Area (m2) 61357 54886 963 lt 001 0078 0257 92 B Variation explained by axes

Axis Individual Cumulative Individual Cumulative

explained variation of fitted model explained variation of total variation

1 9821 9821 2521 2521

2 179 100 046 2567

Mean ocean surface temperature was lowest in spring and highest in summer (January and February) (Figure 3) Mean swell height increased in autumn and peaked in winter with this peak coinciding with an increase in mean salinity recorded in all pools in winter while the highest salinities were recorded in invaded pools (Table S1 Figure 3) There was a clear recruitment event at the onset of spring (AugustSeptember) during which 95 plusmn 49 individuals were recorded per invaded pool (Table S1 Figure 3) This coincided with an increase in mean rainfall (gt 50 mm) and a drop in mean swell height at the end of winter (mean swell height remained at approximately 3 m from August to December)

Significant differences in stromatolite pool abiotic data were detected between seasons and pools (Table 2) No significant differences in abiotic conditions were detected however between invaded and uninvaded pools There were differences among seasons and F enigmaticus presence was greater in spring when temperature TSS and POM were higher in the pools

while swell height was lower and ocean temperature was higher in the study area (Figure 4) The stepwise AICc analysis showed that F enigmaticus abundance exhibited a significant relationship with pool tempera-ture number of substrates and area potentially available for settlement (Table 3) However this three variable model only explained 26 of the total variation in F enigmaticus abundance data

Discussion

Ficopomatus enigmaticus is not an obligate reef builder (Bianchi and Morri 2001) and occurs indivi-dually or in small aggregations in the South African stromatolite pools often attached to rocks directly on stromatolites (Figure 2) or on any other available substrates Availability of settlement substrates and water temperature appear to be the most important variables controlling the persistence of F enigmaticus in stromatolite pools Overall environmental variables explained a low percentage of the variation in F enigmaticus abundance (Table 3) This is expected

Invasive polychaete in marine stromatolites

263

for a habitat generalist with wide environmental tolerance However Schwindt et al (2004a) argued that habitats favoured by F enigmaticus populations are very similar in their physical chemical and biological characteristics throughout the world These authors also suggested that the most important variables that affect the spread of this species in invaded habitats may be salinity nutrients (ie TSS POM and chl-a) and environmental energy (eg current speed or swell height as proxy) The TSS POM and chl-a values measured in the current study correspond with the lowest recorded by Schwindt et al (2004a) and therefore may partially explain the relatively small population size observed in stromatolite pools

The use of estuaries and intermittent water bodies as stepping stones for aquatic organisms is well-documented (Burridge et al 2004 Reynolds et al 2014 Tulbure et al 2014) These environments facilitate spread recruitment and invasion of organisms by providing food (OrsquoSullivan et al 2014) a favourable environment during a shift or an unfavourable time period (Hannah et al 2014) and reducing the distance between suitable habitats for organisms with a mobile life stage (Gaines and Bertness 1992) Perhaps not all these factors are necessary For example habitats with unstable environmental characteristics such as stromatolite pools still appear to create suitable stepping stones for habitat generalists such as the estuarine tubeworm

Ficopomatus enigmaticus exhibits gregarious larval settlement which is strongly affected by the ability of the larvae to recognise adults of their own species (Bianchi and Morri 1996) the nature of the settlement substrate and water flow velocity (Kupriyanova et al 2001) Due to their position and physical structure stromatolite pools maintain relatively constant water levels throughout the year and appear to provide a degree of shelter against strong currents that would disrupt larval settlement In agreement with Thorp (1994) the shallow depth of invaded pools led to the development of elevated temperatures during the reproductive period of F enigmaticus within the stromatolites thereby enhancing larval and adult growth Indeed invaded pools may reach higher temperatures than uninvaded pools and the ocean during which time worm growth could escalate Furthermore when over 95 of the population died in invaded pools in February 2014 a small portion of the population survived and persisted during the entire study period in certain stromatolite pools which acted as refuges for F enigmaticus The cause of the demise of F enigmaticus in February is not certain but was possibly linked to a harmful algal bloom prevailing in the area at that time Red tides can cause hypoxic

Figure 4 PCA showing differences in abiotic data collected during 2014 from four invaded and four uninvaded stromatolite pools The PCA is presented with labels for the different seasons (a) and presenceabsence of F enigmaticus (b) The first two axes explain 374 of the total variance (PC1 = 22 and PC2 = 154)

conditions that would have been lethal to F enigma-ticus even though it is tolerant to low dissolved oxygen (Dittmann et al 2009)

Despite its wide salinity and temperature tolerance range environmental conditions do influence growth rates of F enigmaticus (Bianchi and Morri 1996) Rates of tube length growth vary widely (reviewed in Dittmann et al 2009) In this study the fastest F enigmaticus growth rates and greatest abundances were recorded in stromatolite pools during a mass recruitment event at the onset of Austral spring However tube growth was also not significantly different between seasons Furthermore the presence of empty tubes in some pools suggests that worms have survived in greater numbers in the past Post-settlement growth of F enigmaticus juveniles is very fast and particularly affected by salinity and

NAF Miranda et al

264

temperature (Dittmann et al 2009 and references therein) Once individuals settle they can grow to maturity lengths of 6ndash10 mm in a few weeks although this may vary regionally However temperatures exceeding 20ordmC and salinities of 10ndash30 appear to be optimal for F enigmaticus growth (Tebble 1953) Ficopomatus enigmaticus is sensitive to reductions in temperature (Kupriyanova et al 2001) and as with most invertebrates embryonic and larval development time increases with decreasing temperatures (Kupriyanova et al 2001) The minimum temperature value for spawning can vary among populations and is reported to range from 10 to 17degC (Dittmann et al 2009) During the current study average temperatures as low as 145degC were recorded in the ocean in spring while invaded stromatolite pools had average temperatures gt 20degC which seem to be more favourable for growth and reproduction

Ficopomatus enigmaticus larvae are passively distributed by water currents (Kupriyanova et al 2001) and the source of the spawning event that resulted in the early spring recruitment in stromatolite pools is uncertain Perhaps the increase in temperature in pools reduction in swell height and steady rainfall created the required conditions for successful spawning The source of the larvae may have been the persisting population of large adult worms in the stromatolite pools Alternatively F enigmaticus could be introduced through shipping and mariculture (Glasby et al 2007) attached to debris coming from adjacent estuaries with larger populations and even attached to large mobile organisms such as turtles and crabs Although only one period of spawning and settlement was observed in the current study more periods are possible since different populations exhibit variability in settlement periods and reproductive activity seems to be timed to fit the preferred local conditions (Dittmann et al 2009)

As suggested by Hill (1967) for the closely related Ficopomatus uschakovi (Pillai 1960) F enigmaticus may have different salinity optima for survival growth and reproduction The implication is that salinity fluctuations may be critical for the successful reproduction and development of Ficopomatus (Tebble 1953) Fluctuations in temperature and salinity may also exclude competitors and predators of F enigmaticus allowing them to recruit Deeper pools are more stable in terms of temperature but may also be harder to colonize due to biotic barriers such as increased algal growth competition and predation Limitations on potential settlement substrates can result in the use of any available surfaces including roots or other decomposing plant material which is not ideal as the worms are bound to be dislodged Dislodging may also happen when

worms settle on brittle stromatolite deposits However they may persist for long enough to attract other worms and spawn High rates of predation by crabs and molluscs combined with increased competition for food and space with other benthic organisms may explain the absence of F enigmaticus in lower pools (excluded from analyses in this study) Although only environmental variables were considered in this study biotic factors are also important and should be addressed in future studies

The filter-feeding ability of F enigmaticus is remarkable as it can affect whole ecosystems by removing large amounts of particulate matter from the water column thus affecting primary production by removing phytoplankton potentially ameliorating eutrophication and decreasing overall turbidity (Davies et al 1989 Bruschetti et al 2008) However the F enigmaticus population densities in stromatolite pools are much lower than those in estuaries and lagoons where they form reefs Based on clearance rate estimates of 859 mlmgminus1 dry mass of worm hminus1 (Davies et al 1989) worms in the current study filtered a maximum of 19 L of water per pool per day Although turbidity TSS POM and chl-a were marginally lower in some invaded pools compared to uninvaded pools it remains inconclusive whether the feeding of F enigmaticus had a significant effect in stromatolite pools

Wasson et al (2001) indicated that F enigmaticus and other invasive species can make use of suitable estuarine habitats as ldquostepping stonesrdquo Interestingly invasive species can be transferred via stepping stone habitats with potentially unfavourable environmental conditions (Apte et al 2000) Land-use changes in the past few decades have resulted in the introduction of more artificial structures in aquatic environments and increased dumping of waste especially buoyant plastic into coastal waters both of which have been linked to global increases in the spread and biomass of F enigmaticus (Schwindt et al 2004b McQuaid and Griffiths 2014) and other invasive aquatic species (Airoldi et al 2015 Mesel et al 2015) According to Saura et al (2013) the capacity of species to exploit stepping stones depends on species-specific life-history traits This study shows that F enigmaticus is capable of using small freshwater seepage areas along the South African coastline Havel et al (2005) and Johnson et al (2008) reported that small reservoirs and dams also can facilitate the spread of invasive species into seemingly isolated habitats Similarly perhaps unique ecosystems such as stromatolite pools which provide suitable settlement surfaces serve as stepping stones for the spread of a variety of organisms along the coast including invasive species

Invasive polychaete in marine stromatolites

265

Acknowledgements

This work was supported by the South African Research Chairs Initiative of the Department of Science and Technology (DST) and National Research Foundation (NRF) of South Africa Any opinion finding and conclusion or recommendation expressed in this document is that of the authors and the NRF does not accept any liability in this regard The authors wish to thank the South African Weather Service for providing climate data Windguru for their swell and wave predictions and the South African Environmental Observation Network (SAEON) for providing hourly underwater temperature data for the inshore environment We are also grateful to the anonymous reviewers and to Ryan Reisinger and Chris Oosthuizen for their constructive input which strengthened the paper

References

Airoldi L Turon X Perkol-Finkel S Rius M (2015) Corridors for aliens but not for natives effects of marine urban sprawl at a regional scale Diversity and Distributions 21 755ndash768 httpdxdoiorg101111ddi12301

Anderson MJ Gorley RN Clarke KR (2008) PERMANOVA+ for PRIMER Guide to software and statistical methods PRIMER-E Plymouth UK

Apte S Holland B Godwin LS Gardner JA (2000) Jumping Ship a stepping stone event mediating transfer of a non-indigenous species via a potentially unsuitable environment Biological Invasions 2 75ndash79 httpdxdoiorg101023A1010024818644

Bax N Williamson A Aguero M Gonzalez E Geeves W (2003) Marine invasive alien species a threat to global biodiversity Emerging Issues in Oceans Coasts and Islands 27 313ndash323 httpdxdoiorg101016s0308-597x(03)00041-1

Bellard C Leroy B Thuiller W Rysman J-F Courchamp F (2016) Major drivers of invasion risks throughout the world Ecosphere 7 e01241 httpdxdoiorg101002ecs21241

Bianchi CN Morri C (2001) The battle is not to the strong serpulid reefs in the lagoon of Orbetello (Tuscany Italy) Estuarine Coastal and Shelf Science 53 215ndash220 httpdxdoiorg101006 ecss20010793

Bianchi CN Morri C (1996) Ficopomatus ldquoReefsrdquo in the Po River Delta (Northern Adriatic) their constructional dynamics biology and influences on the brackish-water biota Marine Ecology 17 51ndash66 httpdxdoiorg101111j1439-04851996tb00489x

Blackburn TM Lockwood JL Cassey P (2015) The influence of numbers on invasion success Molecular Ecology 24 1942ndash1953 httpdxdoiorg101111mec13075

Bosak T Knoll AH Petroff AP (2013) The meaning of stromatolites Annual Review of Earth and Planetary Sciences 41 21ndash44 httpdxdoiorg101146annurev-earth-042711-105327

Bruschetti M Luppi T Fanjul E Rosenthal A Iribarne O (2008) Grazing effect of the invasive reef-forming polychaete Ficopomatus enigmaticus (Fauvel) on phytoplankton biomass in a SW Atlantic coastal lagoon Journal of Experimental Marine Biology and Ecology 354 212ndash219 httpdxdoiorg101016 jjembe200711009

Burnham KP Anderson DR (2002) Model selection and multimodel inference a practical information-theoretical approach 2nd ed Springer-Verlag New York

Burridge CP Hurt AC Farrington LW Coutin PC Austin CM (2004) Stepping stone gene flow in an estuarine-dwelling sparid from south-east Australia Journal of Fish Biology 64 805ndash819 httpdxdoiorg101111j1095-864920040347x

Cooper JAG Smith AM Arnscheidt J (2013) Contemporary stromatolite formation in high intertidal rock pools Giants Causeway Northern Ireland preliminary observations In Conley DC Masselink G Russell PE OHare TJ (eds) Proceedings 12th International Coastal Symposium (Plymouth England) pp 1675ndash1680 httpdxdoiorg102112si65-2831

Davies BR Stuart V de Villiers M (1989) The filtration activity of a serpulid polychaete population Ficopomatus enigmaticus (Fauvel) and its effects on water quality in a coastal marina Estuarine Coastal and Shelf Science 29 613ndash620 httpdxdoiorg 1010160272-7714(89)90014-0

Day JH (1951) The polychaete fauna of South Africa Part I The intertidal and estuarine Polychaeta of Natal and Mozambique Annals of the Natal Museum 12 1ndash67

Day JH (1981) Estuarine ecology with particular reference to southern Africa AA Balkema Publishers Netherlands 441 pp

Dittmann S Rolston A Benger SN Kupriyanova EK (2009) Habitat requirements distribution and colonisation of the tubeworm Ficopomatus enigmaticus in the Lower Lakes and Coorong Report for the South Australian Murray-Darling Basin Natural Resources Management Board Adelaide 99 pp

Forbes M Vogwill R Onton K (2010) A characterisation of the coastal tufa deposits of southndashwest Western Australia Sedimentary Geology 232 52ndash65 httpdxdoiorg101016jsedgeo 201009009

Fornos JJ Forteza V Martinez-Taberner A (1997) Modern poly-chaete reefs in Western Mediterranean lagoons Ficopomatus enigmaticus (Fauvel) in the Albufera of Menorca Balearic Islands Palaeogeography Palaeoclimatology Palaeoecology 128 175ndash186 httpdxdoiorg101016S0031-0182(96)00045-4

Gaines SD Bertness MD (1992) Dispersal of juveniles and variable recruitment in sessile marine species Nature 360 579ndash580 httpdxdoiorg101038360579a0

Gallardo B Clavero M Saacutenchez MI Vilagrave M (2016) Global eco-logical impacts of invasive speices in aquatic ecosystems Global Change Biology 22 151ndash163 httpdxdoiorg101111gcb13004

Glasby T Connell S Holloway M Hewitt C (2007) Nonindigenous biota on artificial structures could habitat creation facilitate biological invasions Marine Biology 151 887ndash895 httpdxdoiorg101007s00227-006-0552-5

Grotzinger JP Knoll AH (1999) Stromatolites in precambrian carbonates evolutionary mileposts or environmental dipsticks Annual Review of Earth and Planetary Sciences 27 313ndash358 httpdxdoiorg101146annurevearth271313

Hannah L Flint L Syphard AD Moritz MA Buckley LB McCullough IM (2014) Fine-grain modeling of species response to climate change holdouts stepping-stones and microrefugia Trends in Ecology and Evolution 29 390ndash397 httpdxdoiorg101016jtree201404006

Havel JE Lee CE Zanden MJV (2005) Do reservoirs facilitate invasions into landscapes BioScience 55 518ndash525 httpdxdoiorg1016410006-3568(2005)055[0518DRFIIL]20CO2

Johnson PTJ Olden JD Zanden MJV (2008) Dam invaders impoundments facilitate biological invasions into freshwaters Frontiers in Ecology and the Environment 6 357ndash363 httpdxdoiorg101890070156

Kupriyanova EK Nishi E ten Hove HA Rzhavsky AV (2001) Life-history patterns in serpulimorph polychaetes ecological and evolutionary perspectives Oceangraphy and Marine Biology an Annual Review 39 1ndash101

Lau JA Schultheis EH (2015) When two invasion hypotheses are better than one New Phytologist 205 958ndash960 httpdxdoiorg 101111nph13260

Legendre P Anderson MJ (1999) Distance-based redundancy analysis testing multi-species responses in multi-factorial ecological experiments Ecological Monographs 69 1ndash24 httpdxdoiorg1018900012-9615(1999)069[0001DBRATM]20CO2

McArdle BH Anderson MJ (2001) Fitting multivariate models to community data a comment on distance-based redundancy analysis Ecology 82 290ndash297 httpdxdoiorg10189000129658(20 01)082[0290FMMTCD]20CO2

McQuaid KA Griffiths CL (2014) Alien reef-building polychaete drives long-term changes in invertebrate biomass and diversity in a small urban estuary Estuarine Coastal and Shelf Science 138 101ndash106 httpdxdoiorg101016jecss201312016

Invasive polychaete in marine stromatolites

263

for a habitat generalist with wide environmental tolerance However Schwindt et al (2004a) argued that habitats favoured by F enigmaticus populations are very similar in their physical chemical and biological characteristics throughout the world These authors also suggested that the most important variables that affect the spread of this species in invaded habitats may be salinity nutrients (ie TSS POM and chl-a) and environmental energy (eg current speed or swell height as proxy) The TSS POM and chl-a values measured in the current study correspond with the lowest recorded by Schwindt et al (2004a) and therefore may partially explain the relatively small population size observed in stromatolite pools

The use of estuaries and intermittent water bodies as stepping stones for aquatic organisms is well-documented (Burridge et al 2004 Reynolds et al 2014 Tulbure et al 2014) These environments facilitate spread recruitment and invasion of organisms by providing food (OrsquoSullivan et al 2014) a favourable environment during a shift or an unfavourable time period (Hannah et al 2014) and reducing the distance between suitable habitats for organisms with a mobile life stage (Gaines and Bertness 1992) Perhaps not all these factors are necessary For example habitats with unstable environmental characteristics such as stromatolite pools still appear to create suitable stepping stones for habitat generalists such as the estuarine tubeworm

Ficopomatus enigmaticus exhibits gregarious larval settlement which is strongly affected by the ability of the larvae to recognise adults of their own species (Bianchi and Morri 1996) the nature of the settlement substrate and water flow velocity (Kupriyanova et al 2001) Due to their position and physical structure stromatolite pools maintain relatively constant water levels throughout the year and appear to provide a degree of shelter against strong currents that would disrupt larval settlement In agreement with Thorp (1994) the shallow depth of invaded pools led to the development of elevated temperatures during the reproductive period of F enigmaticus within the stromatolites thereby enhancing larval and adult growth Indeed invaded pools may reach higher temperatures than uninvaded pools and the ocean during which time worm growth could escalate Furthermore when over 95 of the population died in invaded pools in February 2014 a small portion of the population survived and persisted during the entire study period in certain stromatolite pools which acted as refuges for F enigmaticus The cause of the demise of F enigmaticus in February is not certain but was possibly linked to a harmful algal bloom prevailing in the area at that time Red tides can cause hypoxic

Figure 4 PCA showing differences in abiotic data collected during 2014 from four invaded and four uninvaded stromatolite pools The PCA is presented with labels for the different seasons (a) and presenceabsence of F enigmaticus (b) The first two axes explain 374 of the total variance (PC1 = 22 and PC2 = 154)

conditions that would have been lethal to F enigma-ticus even though it is tolerant to low dissolved oxygen (Dittmann et al 2009)

Despite its wide salinity and temperature tolerance range environmental conditions do influence growth rates of F enigmaticus (Bianchi and Morri 1996) Rates of tube length growth vary widely (reviewed in Dittmann et al 2009) In this study the fastest F enigmaticus growth rates and greatest abundances were recorded in stromatolite pools during a mass recruitment event at the onset of Austral spring However tube growth was also not significantly different between seasons Furthermore the presence of empty tubes in some pools suggests that worms have survived in greater numbers in the past Post-settlement growth of F enigmaticus juveniles is very fast and particularly affected by salinity and

NAF Miranda et al

264

temperature (Dittmann et al 2009 and references therein) Once individuals settle they can grow to maturity lengths of 6ndash10 mm in a few weeks although this may vary regionally However temperatures exceeding 20ordmC and salinities of 10ndash30 appear to be optimal for F enigmaticus growth (Tebble 1953) Ficopomatus enigmaticus is sensitive to reductions in temperature (Kupriyanova et al 2001) and as with most invertebrates embryonic and larval development time increases with decreasing temperatures (Kupriyanova et al 2001) The minimum temperature value for spawning can vary among populations and is reported to range from 10 to 17degC (Dittmann et al 2009) During the current study average temperatures as low as 145degC were recorded in the ocean in spring while invaded stromatolite pools had average temperatures gt 20degC which seem to be more favourable for growth and reproduction

Ficopomatus enigmaticus larvae are passively distributed by water currents (Kupriyanova et al 2001) and the source of the spawning event that resulted in the early spring recruitment in stromatolite pools is uncertain Perhaps the increase in temperature in pools reduction in swell height and steady rainfall created the required conditions for successful spawning The source of the larvae may have been the persisting population of large adult worms in the stromatolite pools Alternatively F enigmaticus could be introduced through shipping and mariculture (Glasby et al 2007) attached to debris coming from adjacent estuaries with larger populations and even attached to large mobile organisms such as turtles and crabs Although only one period of spawning and settlement was observed in the current study more periods are possible since different populations exhibit variability in settlement periods and reproductive activity seems to be timed to fit the preferred local conditions (Dittmann et al 2009)

As suggested by Hill (1967) for the closely related Ficopomatus uschakovi (Pillai 1960) F enigmaticus may have different salinity optima for survival growth and reproduction The implication is that salinity fluctuations may be critical for the successful reproduction and development of Ficopomatus (Tebble 1953) Fluctuations in temperature and salinity may also exclude competitors and predators of F enigmaticus allowing them to recruit Deeper pools are more stable in terms of temperature but may also be harder to colonize due to biotic barriers such as increased algal growth competition and predation Limitations on potential settlement substrates can result in the use of any available surfaces including roots or other decomposing plant material which is not ideal as the worms are bound to be dislodged Dislodging may also happen when

worms settle on brittle stromatolite deposits However they may persist for long enough to attract other worms and spawn High rates of predation by crabs and molluscs combined with increased competition for food and space with other benthic organisms may explain the absence of F enigmaticus in lower pools (excluded from analyses in this study) Although only environmental variables were considered in this study biotic factors are also important and should be addressed in future studies

The filter-feeding ability of F enigmaticus is remarkable as it can affect whole ecosystems by removing large amounts of particulate matter from the water column thus affecting primary production by removing phytoplankton potentially ameliorating eutrophication and decreasing overall turbidity (Davies et al 1989 Bruschetti et al 2008) However the F enigmaticus population densities in stromatolite pools are much lower than those in estuaries and lagoons where they form reefs Based on clearance rate estimates of 859 mlmgminus1 dry mass of worm hminus1 (Davies et al 1989) worms in the current study filtered a maximum of 19 L of water per pool per day Although turbidity TSS POM and chl-a were marginally lower in some invaded pools compared to uninvaded pools it remains inconclusive whether the feeding of F enigmaticus had a significant effect in stromatolite pools

Wasson et al (2001) indicated that F enigmaticus and other invasive species can make use of suitable estuarine habitats as ldquostepping stonesrdquo Interestingly invasive species can be transferred via stepping stone habitats with potentially unfavourable environmental conditions (Apte et al 2000) Land-use changes in the past few decades have resulted in the introduction of more artificial structures in aquatic environments and increased dumping of waste especially buoyant plastic into coastal waters both of which have been linked to global increases in the spread and biomass of F enigmaticus (Schwindt et al 2004b McQuaid and Griffiths 2014) and other invasive aquatic species (Airoldi et al 2015 Mesel et al 2015) According to Saura et al (2013) the capacity of species to exploit stepping stones depends on species-specific life-history traits This study shows that F enigmaticus is capable of using small freshwater seepage areas along the South African coastline Havel et al (2005) and Johnson et al (2008) reported that small reservoirs and dams also can facilitate the spread of invasive species into seemingly isolated habitats Similarly perhaps unique ecosystems such as stromatolite pools which provide suitable settlement surfaces serve as stepping stones for the spread of a variety of organisms along the coast including invasive species

Invasive polychaete in marine stromatolites

265

Acknowledgements

This work was supported by the South African Research Chairs Initiative of the Department of Science and Technology (DST) and National Research Foundation (NRF) of South Africa Any opinion finding and conclusion or recommendation expressed in this document is that of the authors and the NRF does not accept any liability in this regard The authors wish to thank the South African Weather Service for providing climate data Windguru for their swell and wave predictions and the South African Environmental Observation Network (SAEON) for providing hourly underwater temperature data for the inshore environment We are also grateful to the anonymous reviewers and to Ryan Reisinger and Chris Oosthuizen for their constructive input which strengthened the paper

References

Airoldi L Turon X Perkol-Finkel S Rius M (2015) Corridors for aliens but not for natives effects of marine urban sprawl at a regional scale Diversity and Distributions 21 755ndash768 httpdxdoiorg101111ddi12301

Anderson MJ Gorley RN Clarke KR (2008) PERMANOVA+ for PRIMER Guide to software and statistical methods PRIMER-E Plymouth UK

Apte S Holland B Godwin LS Gardner JA (2000) Jumping Ship a stepping stone event mediating transfer of a non-indigenous species via a potentially unsuitable environment Biological Invasions 2 75ndash79 httpdxdoiorg101023A1010024818644

Bax N Williamson A Aguero M Gonzalez E Geeves W (2003) Marine invasive alien species a threat to global biodiversity Emerging Issues in Oceans Coasts and Islands 27 313ndash323 httpdxdoiorg101016s0308-597x(03)00041-1

Bellard C Leroy B Thuiller W Rysman J-F Courchamp F (2016) Major drivers of invasion risks throughout the world Ecosphere 7 e01241 httpdxdoiorg101002ecs21241

Bianchi CN Morri C (2001) The battle is not to the strong serpulid reefs in the lagoon of Orbetello (Tuscany Italy) Estuarine Coastal and Shelf Science 53 215ndash220 httpdxdoiorg101006 ecss20010793

Bianchi CN Morri C (1996) Ficopomatus ldquoReefsrdquo in the Po River Delta (Northern Adriatic) their constructional dynamics biology and influences on the brackish-water biota Marine Ecology 17 51ndash66 httpdxdoiorg101111j1439-04851996tb00489x

Blackburn TM Lockwood JL Cassey P (2015) The influence of numbers on invasion success Molecular Ecology 24 1942ndash1953 httpdxdoiorg101111mec13075

Bosak T Knoll AH Petroff AP (2013) The meaning of stromatolites Annual Review of Earth and Planetary Sciences 41 21ndash44 httpdxdoiorg101146annurev-earth-042711-105327

Bruschetti M Luppi T Fanjul E Rosenthal A Iribarne O (2008) Grazing effect of the invasive reef-forming polychaete Ficopomatus enigmaticus (Fauvel) on phytoplankton biomass in a SW Atlantic coastal lagoon Journal of Experimental Marine Biology and Ecology 354 212ndash219 httpdxdoiorg101016 jjembe200711009

Burnham KP Anderson DR (2002) Model selection and multimodel inference a practical information-theoretical approach 2nd ed Springer-Verlag New York

Burridge CP Hurt AC Farrington LW Coutin PC Austin CM (2004) Stepping stone gene flow in an estuarine-dwelling sparid from south-east Australia Journal of Fish Biology 64 805ndash819 httpdxdoiorg101111j1095-864920040347x

Cooper JAG Smith AM Arnscheidt J (2013) Contemporary stromatolite formation in high intertidal rock pools Giants Causeway Northern Ireland preliminary observations In Conley DC Masselink G Russell PE OHare TJ (eds) Proceedings 12th International Coastal Symposium (Plymouth England) pp 1675ndash1680 httpdxdoiorg102112si65-2831

Davies BR Stuart V de Villiers M (1989) The filtration activity of a serpulid polychaete population Ficopomatus enigmaticus (Fauvel) and its effects on water quality in a coastal marina Estuarine Coastal and Shelf Science 29 613ndash620 httpdxdoiorg 1010160272-7714(89)90014-0

Day JH (1951) The polychaete fauna of South Africa Part I The intertidal and estuarine Polychaeta of Natal and Mozambique Annals of the Natal Museum 12 1ndash67

Day JH (1981) Estuarine ecology with particular reference to southern Africa AA Balkema Publishers Netherlands 441 pp

Dittmann S Rolston A Benger SN Kupriyanova EK (2009) Habitat requirements distribution and colonisation of the tubeworm Ficopomatus enigmaticus in the Lower Lakes and Coorong Report for the South Australian Murray-Darling Basin Natural Resources Management Board Adelaide 99 pp

Forbes M Vogwill R Onton K (2010) A characterisation of the coastal tufa deposits of southndashwest Western Australia Sedimentary Geology 232 52ndash65 httpdxdoiorg101016jsedgeo 201009009

Fornos JJ Forteza V Martinez-Taberner A (1997) Modern poly-chaete reefs in Western Mediterranean lagoons Ficopomatus enigmaticus (Fauvel) in the Albufera of Menorca Balearic Islands Palaeogeography Palaeoclimatology Palaeoecology 128 175ndash186 httpdxdoiorg101016S0031-0182(96)00045-4

Gaines SD Bertness MD (1992) Dispersal of juveniles and variable recruitment in sessile marine species Nature 360 579ndash580 httpdxdoiorg101038360579a0

Gallardo B Clavero M Saacutenchez MI Vilagrave M (2016) Global eco-logical impacts of invasive speices in aquatic ecosystems Global Change Biology 22 151ndash163 httpdxdoiorg101111gcb13004

Glasby T Connell S Holloway M Hewitt C (2007) Nonindigenous biota on artificial structures could habitat creation facilitate biological invasions Marine Biology 151 887ndash895 httpdxdoiorg101007s00227-006-0552-5

Grotzinger JP Knoll AH (1999) Stromatolites in precambrian carbonates evolutionary mileposts or environmental dipsticks Annual Review of Earth and Planetary Sciences 27 313ndash358 httpdxdoiorg101146annurevearth271313

Hannah L Flint L Syphard AD Moritz MA Buckley LB McCullough IM (2014) Fine-grain modeling of species response to climate change holdouts stepping-stones and microrefugia Trends in Ecology and Evolution 29 390ndash397 httpdxdoiorg101016jtree201404006

Havel JE Lee CE Zanden MJV (2005) Do reservoirs facilitate invasions into landscapes BioScience 55 518ndash525 httpdxdoiorg1016410006-3568(2005)055[0518DRFIIL]20CO2

Johnson PTJ Olden JD Zanden MJV (2008) Dam invaders impoundments facilitate biological invasions into freshwaters Frontiers in Ecology and the Environment 6 357ndash363 httpdxdoiorg101890070156

Kupriyanova EK Nishi E ten Hove HA Rzhavsky AV (2001) Life-history patterns in serpulimorph polychaetes ecological and evolutionary perspectives Oceangraphy and Marine Biology an Annual Review 39 1ndash101

Lau JA Schultheis EH (2015) When two invasion hypotheses are better than one New Phytologist 205 958ndash960 httpdxdoiorg 101111nph13260

Legendre P Anderson MJ (1999) Distance-based redundancy analysis testing multi-species responses in multi-factorial ecological experiments Ecological Monographs 69 1ndash24 httpdxdoiorg1018900012-9615(1999)069[0001DBRATM]20CO2

McArdle BH Anderson MJ (2001) Fitting multivariate models to community data a comment on distance-based redundancy analysis Ecology 82 290ndash297 httpdxdoiorg10189000129658(20 01)082[0290FMMTCD]20CO2

McQuaid KA Griffiths CL (2014) Alien reef-building polychaete drives long-term changes in invertebrate biomass and diversity in a small urban estuary Estuarine Coastal and Shelf Science 138 101ndash106 httpdxdoiorg101016jecss201312016

NAF Miranda et al

264

temperature (Dittmann et al 2009 and references therein) Once individuals settle they can grow to maturity lengths of 6ndash10 mm in a few weeks although this may vary regionally However temperatures exceeding 20ordmC and salinities of 10ndash30 appear to be optimal for F enigmaticus growth (Tebble 1953) Ficopomatus enigmaticus is sensitive to reductions in temperature (Kupriyanova et al 2001) and as with most invertebrates embryonic and larval development time increases with decreasing temperatures (Kupriyanova et al 2001) The minimum temperature value for spawning can vary among populations and is reported to range from 10 to 17degC (Dittmann et al 2009) During the current study average temperatures as low as 145degC were recorded in the ocean in spring while invaded stromatolite pools had average temperatures gt 20degC which seem to be more favourable for growth and reproduction

Ficopomatus enigmaticus larvae are passively distributed by water currents (Kupriyanova et al 2001) and the source of the spawning event that resulted in the early spring recruitment in stromatolite pools is uncertain Perhaps the increase in temperature in pools reduction in swell height and steady rainfall created the required conditions for successful spawning The source of the larvae may have been the persisting population of large adult worms in the stromatolite pools Alternatively F enigmaticus could be introduced through shipping and mariculture (Glasby et al 2007) attached to debris coming from adjacent estuaries with larger populations and even attached to large mobile organisms such as turtles and crabs Although only one period of spawning and settlement was observed in the current study more periods are possible since different populations exhibit variability in settlement periods and reproductive activity seems to be timed to fit the preferred local conditions (Dittmann et al 2009)

As suggested by Hill (1967) for the closely related Ficopomatus uschakovi (Pillai 1960) F enigmaticus may have different salinity optima for survival growth and reproduction The implication is that salinity fluctuations may be critical for the successful reproduction and development of Ficopomatus (Tebble 1953) Fluctuations in temperature and salinity may also exclude competitors and predators of F enigmaticus allowing them to recruit Deeper pools are more stable in terms of temperature but may also be harder to colonize due to biotic barriers such as increased algal growth competition and predation Limitations on potential settlement substrates can result in the use of any available surfaces including roots or other decomposing plant material which is not ideal as the worms are bound to be dislodged Dislodging may also happen when

worms settle on brittle stromatolite deposits However they may persist for long enough to attract other worms and spawn High rates of predation by crabs and molluscs combined with increased competition for food and space with other benthic organisms may explain the absence of F enigmaticus in lower pools (excluded from analyses in this study) Although only environmental variables were considered in this study biotic factors are also important and should be addressed in future studies

The filter-feeding ability of F enigmaticus is remarkable as it can affect whole ecosystems by removing large amounts of particulate matter from the water column thus affecting primary production by removing phytoplankton potentially ameliorating eutrophication and decreasing overall turbidity (Davies et al 1989 Bruschetti et al 2008) However the F enigmaticus population densities in stromatolite pools are much lower than those in estuaries and lagoons where they form reefs Based on clearance rate estimates of 859 mlmgminus1 dry mass of worm hminus1 (Davies et al 1989) worms in the current study filtered a maximum of 19 L of water per pool per day Although turbidity TSS POM and chl-a were marginally lower in some invaded pools compared to uninvaded pools it remains inconclusive whether the feeding of F enigmaticus had a significant effect in stromatolite pools

Wasson et al (2001) indicated that F enigmaticus and other invasive species can make use of suitable estuarine habitats as ldquostepping stonesrdquo Interestingly invasive species can be transferred via stepping stone habitats with potentially unfavourable environmental conditions (Apte et al 2000) Land-use changes in the past few decades have resulted in the introduction of more artificial structures in aquatic environments and increased dumping of waste especially buoyant plastic into coastal waters both of which have been linked to global increases in the spread and biomass of F enigmaticus (Schwindt et al 2004b McQuaid and Griffiths 2014) and other invasive aquatic species (Airoldi et al 2015 Mesel et al 2015) According to Saura et al (2013) the capacity of species to exploit stepping stones depends on species-specific life-history traits This study shows that F enigmaticus is capable of using small freshwater seepage areas along the South African coastline Havel et al (2005) and Johnson et al (2008) reported that small reservoirs and dams also can facilitate the spread of invasive species into seemingly isolated habitats Similarly perhaps unique ecosystems such as stromatolite pools which provide suitable settlement surfaces serve as stepping stones for the spread of a variety of organisms along the coast including invasive species

Invasive polychaete in marine stromatolites

265

Acknowledgements

This work was supported by the South African Research Chairs Initiative of the Department of Science and Technology (DST) and National Research Foundation (NRF) of South Africa Any opinion finding and conclusion or recommendation expressed in this document is that of the authors and the NRF does not accept any liability in this regard The authors wish to thank the South African Weather Service for providing climate data Windguru for their swell and wave predictions and the South African Environmental Observation Network (SAEON) for providing hourly underwater temperature data for the inshore environment We are also grateful to the anonymous reviewers and to Ryan Reisinger and Chris Oosthuizen for their constructive input which strengthened the paper

References

Airoldi L Turon X Perkol-Finkel S Rius M (2015) Corridors for aliens but not for natives effects of marine urban sprawl at a regional scale Diversity and Distributions 21 755ndash768 httpdxdoiorg101111ddi12301

Anderson MJ Gorley RN Clarke KR (2008) PERMANOVA+ for PRIMER Guide to software and statistical methods PRIMER-E Plymouth UK

Apte S Holland B Godwin LS Gardner JA (2000) Jumping Ship a stepping stone event mediating transfer of a non-indigenous species via a potentially unsuitable environment Biological Invasions 2 75ndash79 httpdxdoiorg101023A1010024818644

Bax N Williamson A Aguero M Gonzalez E Geeves W (2003) Marine invasive alien species a threat to global biodiversity Emerging Issues in Oceans Coasts and Islands 27 313ndash323 httpdxdoiorg101016s0308-597x(03)00041-1

Bellard C Leroy B Thuiller W Rysman J-F Courchamp F (2016) Major drivers of invasion risks throughout the world Ecosphere 7 e01241 httpdxdoiorg101002ecs21241

Bianchi CN Morri C (2001) The battle is not to the strong serpulid reefs in the lagoon of Orbetello (Tuscany Italy) Estuarine Coastal and Shelf Science 53 215ndash220 httpdxdoiorg101006 ecss20010793

Bianchi CN Morri C (1996) Ficopomatus ldquoReefsrdquo in the Po River Delta (Northern Adriatic) their constructional dynamics biology and influences on the brackish-water biota Marine Ecology 17 51ndash66 httpdxdoiorg101111j1439-04851996tb00489x

Blackburn TM Lockwood JL Cassey P (2015) The influence of numbers on invasion success Molecular Ecology 24 1942ndash1953 httpdxdoiorg101111mec13075

Bosak T Knoll AH Petroff AP (2013) The meaning of stromatolites Annual Review of Earth and Planetary Sciences 41 21ndash44 httpdxdoiorg101146annurev-earth-042711-105327

Bruschetti M Luppi T Fanjul E Rosenthal A Iribarne O (2008) Grazing effect of the invasive reef-forming polychaete Ficopomatus enigmaticus (Fauvel) on phytoplankton biomass in a SW Atlantic coastal lagoon Journal of Experimental Marine Biology and Ecology 354 212ndash219 httpdxdoiorg101016 jjembe200711009

Burnham KP Anderson DR (2002) Model selection and multimodel inference a practical information-theoretical approach 2nd ed Springer-Verlag New York

Burridge CP Hurt AC Farrington LW Coutin PC Austin CM (2004) Stepping stone gene flow in an estuarine-dwelling sparid from south-east Australia Journal of Fish Biology 64 805ndash819 httpdxdoiorg101111j1095-864920040347x

Cooper JAG Smith AM Arnscheidt J (2013) Contemporary stromatolite formation in high intertidal rock pools Giants Causeway Northern Ireland preliminary observations In Conley DC Masselink G Russell PE OHare TJ (eds) Proceedings 12th International Coastal Symposium (Plymouth England) pp 1675ndash1680 httpdxdoiorg102112si65-2831

Davies BR Stuart V de Villiers M (1989) The filtration activity of a serpulid polychaete population Ficopomatus enigmaticus (Fauvel) and its effects on water quality in a coastal marina Estuarine Coastal and Shelf Science 29 613ndash620 httpdxdoiorg 1010160272-7714(89)90014-0

Day JH (1951) The polychaete fauna of South Africa Part I The intertidal and estuarine Polychaeta of Natal and Mozambique Annals of the Natal Museum 12 1ndash67

Day JH (1981) Estuarine ecology with particular reference to southern Africa AA Balkema Publishers Netherlands 441 pp

Dittmann S Rolston A Benger SN Kupriyanova EK (2009) Habitat requirements distribution and colonisation of the tubeworm Ficopomatus enigmaticus in the Lower Lakes and Coorong Report for the South Australian Murray-Darling Basin Natural Resources Management Board Adelaide 99 pp

Forbes M Vogwill R Onton K (2010) A characterisation of the coastal tufa deposits of southndashwest Western Australia Sedimentary Geology 232 52ndash65 httpdxdoiorg101016jsedgeo 201009009

Fornos JJ Forteza V Martinez-Taberner A (1997) Modern poly-chaete reefs in Western Mediterranean lagoons Ficopomatus enigmaticus (Fauvel) in the Albufera of Menorca Balearic Islands Palaeogeography Palaeoclimatology Palaeoecology 128 175ndash186 httpdxdoiorg101016S0031-0182(96)00045-4

Gaines SD Bertness MD (1992) Dispersal of juveniles and variable recruitment in sessile marine species Nature 360 579ndash580 httpdxdoiorg101038360579a0

Gallardo B Clavero M Saacutenchez MI Vilagrave M (2016) Global eco-logical impacts of invasive speices in aquatic ecosystems Global Change Biology 22 151ndash163 httpdxdoiorg101111gcb13004

Glasby T Connell S Holloway M Hewitt C (2007) Nonindigenous biota on artificial structures could habitat creation facilitate biological invasions Marine Biology 151 887ndash895 httpdxdoiorg101007s00227-006-0552-5

Grotzinger JP Knoll AH (1999) Stromatolites in precambrian carbonates evolutionary mileposts or environmental dipsticks Annual Review of Earth and Planetary Sciences 27 313ndash358 httpdxdoiorg101146annurevearth271313

Hannah L Flint L Syphard AD Moritz MA Buckley LB McCullough IM (2014) Fine-grain modeling of species response to climate change holdouts stepping-stones and microrefugia Trends in Ecology and Evolution 29 390ndash397 httpdxdoiorg101016jtree201404006

Havel JE Lee CE Zanden MJV (2005) Do reservoirs facilitate invasions into landscapes BioScience 55 518ndash525 httpdxdoiorg1016410006-3568(2005)055[0518DRFIIL]20CO2

Johnson PTJ Olden JD Zanden MJV (2008) Dam invaders impoundments facilitate biological invasions into freshwaters Frontiers in Ecology and the Environment 6 357ndash363 httpdxdoiorg101890070156

Kupriyanova EK Nishi E ten Hove HA Rzhavsky AV (2001) Life-history patterns in serpulimorph polychaetes ecological and evolutionary perspectives Oceangraphy and Marine Biology an Annual Review 39 1ndash101

Lau JA Schultheis EH (2015) When two invasion hypotheses are better than one New Phytologist 205 958ndash960 httpdxdoiorg 101111nph13260

Legendre P Anderson MJ (1999) Distance-based redundancy analysis testing multi-species responses in multi-factorial ecological experiments Ecological Monographs 69 1ndash24 httpdxdoiorg1018900012-9615(1999)069[0001DBRATM]20CO2

McArdle BH Anderson MJ (2001) Fitting multivariate models to community data a comment on distance-based redundancy analysis Ecology 82 290ndash297 httpdxdoiorg10189000129658(20 01)082[0290FMMTCD]20CO2

McQuaid KA Griffiths CL (2014) Alien reef-building polychaete drives long-term changes in invertebrate biomass and diversity in a small urban estuary Estuarine Coastal and Shelf Science 138 101ndash106 httpdxdoiorg101016jecss201312016

Invasive polychaete in marine stromatolites

265

Acknowledgements

This work was supported by the South African Research Chairs Initiative of the Department of Science and Technology (DST) and National Research Foundation (NRF) of South Africa Any opinion finding and conclusion or recommendation expressed in this document is that of the authors and the NRF does not accept any liability in this regard The authors wish to thank the South African Weather Service for providing climate data Windguru for their swell and wave predictions and the South African Environmental Observation Network (SAEON) for providing hourly underwater temperature data for the inshore environment We are also grateful to the anonymous reviewers and to Ryan Reisinger and Chris Oosthuizen for their constructive input which strengthened the paper

References

Airoldi L Turon X Perkol-Finkel S Rius M (2015) Corridors for aliens but not for natives effects of marine urban sprawl at a regional scale Diversity and Distributions 21 755ndash768 httpdxdoiorg101111ddi12301

Anderson MJ Gorley RN Clarke KR (2008) PERMANOVA+ for PRIMER Guide to software and statistical methods PRIMER-E Plymouth UK

Apte S Holland B Godwin LS Gardner JA (2000) Jumping Ship a stepping stone event mediating transfer of a non-indigenous species via a potentially unsuitable environment Biological Invasions 2 75ndash79 httpdxdoiorg101023A1010024818644

Bax N Williamson A Aguero M Gonzalez E Geeves W (2003) Marine invasive alien species a threat to global biodiversity Emerging Issues in Oceans Coasts and Islands 27 313ndash323 httpdxdoiorg101016s0308-597x(03)00041-1

Bellard C Leroy B Thuiller W Rysman J-F Courchamp F (2016) Major drivers of invasion risks throughout the world Ecosphere 7 e01241 httpdxdoiorg101002ecs21241

Bianchi CN Morri C (2001) The battle is not to the strong serpulid reefs in the lagoon of Orbetello (Tuscany Italy) Estuarine Coastal and Shelf Science 53 215ndash220 httpdxdoiorg101006 ecss20010793

Bianchi CN Morri C (1996) Ficopomatus ldquoReefsrdquo in the Po River Delta (Northern Adriatic) their constructional dynamics biology and influences on the brackish-water biota Marine Ecology 17 51ndash66 httpdxdoiorg101111j1439-04851996tb00489x

Blackburn TM Lockwood JL Cassey P (2015) The influence of numbers on invasion success Molecular Ecology 24 1942ndash1953 httpdxdoiorg101111mec13075

Bosak T Knoll AH Petroff AP (2013) The meaning of stromatolites Annual Review of Earth and Planetary Sciences 41 21ndash44 httpdxdoiorg101146annurev-earth-042711-105327

Bruschetti M Luppi T Fanjul E Rosenthal A Iribarne O (2008) Grazing effect of the invasive reef-forming polychaete Ficopomatus enigmaticus (Fauvel) on phytoplankton biomass in a SW Atlantic coastal lagoon Journal of Experimental Marine Biology and Ecology 354 212ndash219 httpdxdoiorg101016 jjembe200711009

Burnham KP Anderson DR (2002) Model selection and multimodel inference a practical information-theoretical approach 2nd ed Springer-Verlag New York

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Davies BR Stuart V de Villiers M (1989) The filtration activity of a serpulid polychaete population Ficopomatus enigmaticus (Fauvel) and its effects on water quality in a coastal marina Estuarine Coastal and Shelf Science 29 613ndash620 httpdxdoiorg 1010160272-7714(89)90014-0

Day JH (1951) The polychaete fauna of South Africa Part I The intertidal and estuarine Polychaeta of Natal and Mozambique Annals of the Natal Museum 12 1ndash67

Day JH (1981) Estuarine ecology with particular reference to southern Africa AA Balkema Publishers Netherlands 441 pp

Dittmann S Rolston A Benger SN Kupriyanova EK (2009) Habitat requirements distribution and colonisation of the tubeworm Ficopomatus enigmaticus in the Lower Lakes and Coorong Report for the South Australian Murray-Darling Basin Natural Resources Management Board Adelaide 99 pp

Forbes M Vogwill R Onton K (2010) A characterisation of the coastal tufa deposits of southndashwest Western Australia Sedimentary Geology 232 52ndash65 httpdxdoiorg101016jsedgeo 201009009

Fornos JJ Forteza V Martinez-Taberner A (1997) Modern poly-chaete reefs in Western Mediterranean lagoons Ficopomatus enigmaticus (Fauvel) in the Albufera of Menorca Balearic Islands Palaeogeography Palaeoclimatology Palaeoecology 128 175ndash186 httpdxdoiorg101016S0031-0182(96)00045-4

Gaines SD Bertness MD (1992) Dispersal of juveniles and variable recruitment in sessile marine species Nature 360 579ndash580 httpdxdoiorg101038360579a0

Gallardo B Clavero M Saacutenchez MI Vilagrave M (2016) Global eco-logical impacts of invasive speices in aquatic ecosystems Global Change Biology 22 151ndash163 httpdxdoiorg101111gcb13004

Glasby T Connell S Holloway M Hewitt C (2007) Nonindigenous biota on artificial structures could habitat creation facilitate biological invasions Marine Biology 151 887ndash895 httpdxdoiorg101007s00227-006-0552-5

Grotzinger JP Knoll AH (1999) Stromatolites in precambrian carbonates evolutionary mileposts or environmental dipsticks Annual Review of Earth and Planetary Sciences 27 313ndash358 httpdxdoiorg101146annurevearth271313

Hannah L Flint L Syphard AD Moritz MA Buckley LB McCullough IM (2014) Fine-grain modeling of species response to climate change holdouts stepping-stones and microrefugia Trends in Ecology and Evolution 29 390ndash397 httpdxdoiorg101016jtree201404006

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Johnson PTJ Olden JD Zanden MJV (2008) Dam invaders impoundments facilitate biological invasions into freshwaters Frontiers in Ecology and the Environment 6 357ndash363 httpdxdoiorg101890070156

Kupriyanova EK Nishi E ten Hove HA Rzhavsky AV (2001) Life-history patterns in serpulimorph polychaetes ecological and evolutionary perspectives Oceangraphy and Marine Biology an Annual Review 39 1ndash101

Lau JA Schultheis EH (2015) When two invasion hypotheses are better than one New Phytologist 205 958ndash960 httpdxdoiorg 101111nph13260

Legendre P Anderson MJ (1999) Distance-based redundancy analysis testing multi-species responses in multi-factorial ecological experiments Ecological Monographs 69 1ndash24 httpdxdoiorg1018900012-9615(1999)069[0001DBRATM]20CO2

McArdle BH Anderson MJ (2001) Fitting multivariate models to community data a comment on distance-based redundancy analysis Ecology 82 290ndash297 httpdxdoiorg10189000129658(20 01)082[0290FMMTCD]20CO2

McQuaid KA Griffiths CL (2014) Alien reef-building polychaete drives long-term changes in invertebrate biomass and diversity in a small urban estuary Estuarine Coastal and Shelf Science 138 101ndash106 httpdxdoiorg101016jecss201312016

NAF Miranda et al

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Mead A Carlton JT Griffiths CL Rius M (2011a) The introduced and cryptogenic marine and estuarine species of South Africa Journal of Natural History 45 2463ndash2524 httpdxdoiorg101080 002229332011595836

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Schwindt E Iribarne OO Isla FI (2004b) Physical effects of an invading reef-building polychaete on an Argentinean estuarine environment Estuarine Coastal and Shelf Science 59 109ndash120 httpdxdoiorg101016jecss200306004

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encrustation by a tubed marine worm Journal of the Institution of Municipal Engineers 80 259ndash265

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Thorp CH (1994) Population variation in Ficopomatus enigmaticus (Fauvel) (Polychaeta Serpulidae) in a brackish water millpond at Emsworth West Sussex UK Meacutemoires du Museacuteum National dHistoire Naturelle 162 585ndash591

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Wasson K Zabin CJ Bedinger L Diaz MC Pearse JS (2001) Biological invasions of estuaries without international shipping the importance of intraregional transport Biological Conse-rvation 102 143ndash153 httpdxdoiorg101016S0006-3207(01)00098-2

Supplementary material

The following supplementary material is available for this article

Table S1 Mean values of abiotic data collected during 2014 from four stromatolite pools invaded by F enigmaticus and four uninvaded pools

This material is available as part of online article from httpwwwaquaticinvasionsnet2016SupplementsAI_2016_Miranda_etal_Supplementxls