Do otolith increments allow correct inferences about age and growth of coral reef fishes?

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    Do otolith increments allow correct inferences about ageand growth of coral reef fishes?

    D. J. Booth

    Received: 10 June 2013 / Accepted: 12 November 2013 / Published online: 23 November 2013

    Springer-Verlag Berlin Heidelberg 2013

    Abstract Otolith increment structure is widely used to

    estimate age and growth of marine fishes. Here, I test the

    accuracy of the long-term otolith increment analysis of the

    lemon damselfish Pomacentrus moluccensis to describe

    age and growth characteristics. I compare the number of

    putative annual otolith increments (as a proxy for actual

    age) and widths of these increments (as proxies for somatic

    growth) with actual tagged fish-length data, based on a

    6-year dataset, the longest time course for a coral reef fish.

    Estimated age from otoliths corresponded closely with

    actual age in all cases, confirming annual increment for-

    mation. However, otolith increment widths were poor

    proxies for actual growth in length [linear regression

    r2 = 0.440.90, n = 6 fish] and were clearly of limited

    value in estimating annual growth. Up to 60 % of the

    annual growth variation was missed using otolith incre-

    ments, suggesting the long-term back calculations of oto-

    lith growth characteristics of reef fish populations should

    be interpreted with caution.

    Keywords Age validation Coral reef damselfish Growth Otolith back calculation Otolith increments Pomacentrus moluccensis

    Introduction

    A key goal of ecological research is to understand how

    species vary in their persistence. Performance measures

    include survivorship and growth, and studies often assess

    how these demographic parameters vary temporally and

    spatially. For marine fishes, a structure often used to

    hindcast survival and growth is the otolith or earstone,

    which accretes rings that have been calibrated both as

    annual (Fowler and Short 1998) and daily (Panella 1971).

    Validation of these rings as annual can be done in the

    laboratory by staining otoliths and holding fish for over a

    year, or in the field using a marginal otolith increment

    approach (Fowler and Short 1998) or by comparing with

    known age of a tagged fish. The latter is the most reliable

    but is rarely done since it requires a long-term (multiyear)

    field monitoring program. Shorter-term field annual ring

    validation consisted of marking the fish with a vital stain

    such as tetracycline and recapturing the fish after 12 years

    (e.g., Fowler and Short 1998) and thus cannot be applied to

    the entire life span of longer lived fish.

    More recently, the size of increments between otolith

    rings has been used as a proxy for somatic growth,

    allowing individual and population trajectories of growth

    to be assessed (Campana 1990). Field time is also mini-

    mized compared to mark-recapture, and a selection of

    cohorts can be sampled at each site by sampling otoliths at

    one point in time. However, assumptions of daily and

    annual formation of rings and use of increments as growth

    proxies have to be validated (Campana 1990). Regarding

    the use of otolith increments as proxies for growth stanzas,

    studies have shown that increments can decouple for

    somatic growth, for short or longer periods (e.g., Wright

    et al. 1990). While a number of statistical assumptions

    must go into choice of back calculation model, validation

    Communicated by Biology Editor Dr. Glenn Almany

    D. J. Booth (&)School of the Environment, University of Technology, Sydney,

    PO Box 123, Broadway, NSW 2007, Australia

    e-mail: david.booth@uts.edu.au

    123

    Coral Reefs (2014) 33:255258

    DOI 10.1007/s00338-013-1105-2

  • of how otolith growth relates to somatic growth is often

    lacking (Vigliola et al. 2000).

    Here, based on a long-term study on the Great Barrier

    Reef of a common coral reef damselfish (Pomacentrus

    moluccensis), I ground-truth otolith-based estimates of

    longevity and growth against actual data from tagged fish.

    Materials and methods

    I tagged fish at two sites in and adjacent to One Tree Island

    lagoon, in the southern Great Barrier Reef (23300S,152060E) as part of a long-term study of spatial andtemporal demographics. Cohorts of newly recruited fish

    (size = 15 mm TL on average; 2535 days post-hatching

    after planktonic larval dispersal) were tagged with Visual

    Implant Flourescent Elastomer paint and individuals mea-

    sured (total length, TL mm) and followed annually. As a

    part of the study, commenced in 2000, I recaptured fish and

    recorded body length annually (mm TL). Six tagged fish

    were recaptured and killed in 2006 (2 from one site and 4

    from another) and measured in situ. Fish were collected

    using SCUBA and with clove oil anaesthetic, and frozen

    for transport to the University of Technology, Sydney,

    where otoliths (sagittae) were removed by dissection and

    stored dry until ready for processing. Otoliths were ground

    to the primordium using 3 lm lapping film; wet polishedwith a PMT 08A-10 multiflex 8 diameter polishing cloth

    using 0.020.06 lm colloidal silica on a Kent 3auto-matic polishing unit; and then etched using a 5 % solution

    of EDTA (ethylenedinitrilo tetra acetic acid). Prepared

    otoliths were viewed at 40809 on an Olympus BH2-

    RFCA compound microscope, images stored, and putative

    annual increments counted. The number of growth incre-

    ments was counted along the most visible axis of the otolith

    three times, with the mean taken as the age of the fish. If

    counts differed by more than 5 %, otoliths were reexam-

    ined and if subsequent counts again varied by over 5 %,

    otoliths were rejected (sensu Campana and Neilson 1982).

    Increment widths (primordium to putative Year One

    Increment, Year One to Year Two Increment, etc.) were

    measured along a consistent axis in microns, from the

    digital images using Image J software.

    Results and discussion

    The same six fish that had been externally tagged soon after

    settlement were monitored yearly for body size and col-

    lected at year six for otolith age determination and mea-

    surement of growth increments. First, putative annual age

    rings on otoliths of P. moluccensis were validated, i.e., for

    all six fish that were recaptured after 6 years, there were 6

    opaque zones. Second, for each fish, the relationship

    between annual actual somatic growth (mm TL) and otolith

    increment width was plotted. If otolith increment width

    was a perfect proxy for somatic growth, an r2 approaching

    1 was expected. A pooled r2 of 0.61 indicated a poor

    predictive value overall of otolith increment width for

    somatic growth (Fig. 1). For each fish, r2 varied from 0.44

    to 0.90. In addition, Fig. 1 shows that otolith growth was

    positive even in years where fish exhibited no or negative

    growth in length (see also Caldow and Wellington 2003).

    Figure 2 shows that how annual variation in somatic

    growth and otolith increment width changes across 6 years

    for each of the 6 tagged fish. Clearly, increment width

    patterns are poor proxies of actual somatic growth (length)

    patterns for all fish. Campana (1990) corrected biases

    associated with proportionally larger otoliths for slower-

    growing individuals, but clearly, such corrections would

    not rectify the large mismatch between increment widths

    and somatic growth demonstrated here. Wright et al.

    (1990) demonstrated otolith/somatic growth decoupling in

    salmon was likely due to metabolic differences among

    individuals, with slow growers having a relatively higher

    increment width for a given somatic growth, and this may

    be occurring in the present study where otolith annual

    increments of at least 5 lm were seen even in fish that didnot grow (Fig. 1). However, it still does not explain the

    poor relationship within an individual fish.

    Using the long-term tag monitoring, annual formation of

    otolith rings of a common coral reef damselfish, P. mo-

    luccensis, was validated at one location. This confirms one-

    year tetracycline validations for this species (Fowler and

    Doherty 1992) and shows ontogenetic and spatial consis-

    tency. However, the use of otolith increment width as a proxy

    for somatic growth was not accurate. Over 60 % error can be

    expected for this species where otolith increment width is

    Fig. 1 Relationships between actual annual growth (mm year-1) andotolith annual increment width (lm) for 6 tagged P. moluccensis

    256 Coral Reefs (2014) 33:255258

    123

  • used to indicate annual growth patterns. In addition, several

    studies have noted more difficulty in interpreting otolith

    growth rings from fish in tropical versus temperate marine

    environments (e.g., for damselfishes: Caldow and Welling-

    ton 2003, and see Morales-Nin and Panfili 2005 for a

    review). Therefore, commonly used otolith back calculation

    estimates of fish growth on coral reefs should be used with

    caution at both the individual and population level. Given the

    importance of demographic models in conservation and

    management of reef fishes, more emphasis should be given to

    understand the role and biases associated with common uses

    for otolith information in this context.

    Acknowledgments I would like to thank Gigi Beretta, Will Figueira,and Ralph Alquezar for their help in monitoring and capturing fish and

    the staff of One Tree Island Research Station for their support. Many

    thanks to Kerryn Parkinson for her expert assistance with otolith

    preparations and to Ash Fowler for comments on the draft manuscript.

    This is contribution 119 of the Sydney Institute of Marine Sciences.

    (a)

    (b)

    (c)

    (d)

    (e)

    (f)

    Fig. 2 Annual change in growth of six tagged P. moluccensis (mm year-1, dotted line) versus otolith annual increment width (lm, solid line)

    Coral Reefs (2014) 33:255258 257

    123

  • References

    Caldow C, Wellington GM (2003) Patterns of annual increment

    formation in otoliths of pomacentrids in the tropical western

    Atlantic: implications for population age-structure examination.

    Mar Ecol Prog Ser 265:185195

    Campana SE (1990) How reliable are growth back-calculations based

    on otoliths? Can J Fish Aquat Sci 47:22192227

    Campana SE, Neilson JD (1982) Daily growth increments in otoliths

    of Starry Flounder (Platichthys stellatus) and the influence of

    some environmental variables in their production. Can J Fish

    Aquat Sci 39:937942

    Fowler AJ, Doherty PJ (1992) Validation of annual growth

    increments in the otoliths of two species of damselfish from

    the Southern Great Barrier Reef. Aust J Mar Freshw Res

    43:10571068

    Fowler AJ, Short DA (1998) Validation of age determination from

    otoliths of the King George whiting Sillaginodes punctata

    (Perciformes). Mar Biol 130:577587

    Morales-Nin B, Panfili J (2005) Seasonality on the deep-sea and

    tropics revisited: what can otoliths tell us? Mar Freshw Res

    56:585598

    Panella G (1971) Fish otoliths: Daily growth layers and periodical

    patterns. Science 173:11241126

    Vigliola L, Harmelin-Vivien M, Meekan MG (2000) Comparison of

    techniques of back-calculation of growth and settlement marks

    from the otoliths of three species of Diplodus from the

    Mediterranean Sea. Can J Fish Aquat Sci 57:12911299

    Wright PJ, Metcalfe NB, Thorpe JE (1990) Otolith and somatic

    growth rates in Atlantic salmon parr, Salmo salar L: evidence

    against coupling. J Fish Biol 36:241249

    258 Coral Reefs (2014) 33:255258

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    Do otolith increments allow correct inferences about age and growth of coral reef fishes?AbstractIntroductionMaterials and methodsResults and discussionAcknowledgmentsReferences

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