A Preliminary Study on the Population Characteristics of ...journals.tubitak.gov.tr/zoology/issues/zoo-07-31-4/zoo-31-4-17-0611-15.pdf · (Levantin Denizi, Do¤u Akdeniz) Populasyon

Introduction

Human-mediated species introduction is one of themajor factors adversely affecting biological diversity(Elton, 1958). Although there is an increasing awarenessof this problem at local and global levels, preventing thespread of and eradicating alien species is becomingdifficult as global trade by shipping increases daily andmany alien species have already achieved perpetuatingpopulations in the Mediterranean. In all, 749 alien speciesare known from the Mediterranean Sea (Zenetos et al.,2005) and 277 from the Turkish coasts (Çinar et al.,

2005). The main route of introduction of these species tothe Mediterranean is by shipping and via the Suez Canal.

Pseudonereis anomala Gravier, 1901, a Lessepsianspecies (i.e. a species that migrated from the Red Sea tothe Mediterranean Sea through the Suez Canal), is knownto have been well-acclimated to environmental conditionsof the eastern Mediterranean (Ben-Eliahu, 1975; Çinarand Ergen, 1995). It is a common species in hard-bottomcommunities in the Red Sea, and the Indian and Pacificoceans (Wu et al., 1985). In the Mediterranean Sea, thisspecies was first reported by Fauvel (1937) (off

Turk J Zool31 (2007) 403-410 © TÜB‹TAK

403

A Preliminary Study on the Population Characteristics of theLessepsian Species Pseudonereis anomala (Polychaeta: Nereididae)

in ‹skenderun Bay (Levantine Sea, Eastern Mediterranean)

Melih Ertan ÇINAR*, Cem ALTUN

Ege University, Faculty of Fisheries, Department of Hydrobiology, 35100 Bornova, ‹zmir - TURKEY

Received: 21.11.2006

Abstract: The present paper deals with the population structure and biology of Pseudonereis anomala collected from differentshallow-water habitats of ‹skenderun Bay in September 2005. In all, 434 specimens of P. anomala were found in the area. Themaximum density and biomass values of the species in the area were 2475 ind. m-2 (on Jania rubens) and 7.85 g m-2 (among thebivalve Brachidontes pharaonis), respectively. The relationships among the biometrical measurements of the P. anomala specimenswere assessed using regression and correlation analyses. The growth of P. anomala seems to be allometric. Among the specimensexamined, only one specimen had immature oocytes. Only plant remnants were found in the digestive tracts of the dissectedspecimens.

Key Words: Pseudonereis anomala, Nereididae, Polychaeta, Lessepsian, population structure, Levantine Sea, Turkey

Lessepsian Tür Pseudonereis anomala’n›n (Polychaeta: Nereididae) ‹skenderun Körfezi’ndeki(Levantin Denizi, Do¤u Akdeniz) Populasyon Özellikleri Üzerine Bir Ön Çal›flma

Özet: Bu çal›flma, Eylül 2005’de ‹skenderun Körfezi’nin çeflitli k›y›sal habitatlar›ndan toplanan Pseudonereis anomala’n›n populasyonyap›s›n› ve biyolojisini ele almaktad›r. Bölgede P.anomala’ya ait toplam 434 birey bulunmufltur. Bu türün bölgedeki azami yo¤unlukve biyokütle de¤erleri s›ras›yla 2475 birey m-2 (istasyon K1, Jania rubens üzerinde) ve 7,85 g m-2 (istasyon K5, Brachidontespharaonis üzerinde) olarak bulunmufltur. ‹skenderun Körfezi’ndeki P. anomala bireylerinin biyometrik ölçümleri aras›ndaki iliflkiler,regresyon ve korelasyon analizleri kullan›larak saptanm›flt›r. P. anomala’n›n büyümesi muhtemelen allometriktir. ‹ncelenen bireyleraras›nda, sadece bir bireyin olgun olmayan yumurtalar tafl›d›¤› bulunmufltur. Disekte edilen bireylerin sindirim kanallar›nda sadecebitki kal›nt›lar› bulunmufltur.

Anahtar Sözcükler: Pseudonereis anomala, Nereididae, Polychaeta, Lessepsian, populasyon yap›s›, Levantin Denizi, Türkiye

* E-mail: [email protected]

Alexandria, Egypt) and subsequently was found along theIsraeli coast (Fauvel, 1955; Ben-Eliahu, 1975), theLebanese coast (Laubier, 1966), the Cypriot coast (Ben-Eliahu, 1972; Çinar, 2005), and the Turkish Levantinecoast (Ben-Eliahu, 1989; Ergen and Çinar, 1997).Recently, this species was found off the Turkish andGreek coasts of the Aegean and Ionian Seas (Çinar andErgen, 2005; Kambouroglou and Nicolaidou, 2006).Clearly, this species has become an important invasivecomponent of shallow-water benthic communities of theeastern Mediterranean; however, no study has yetfocused on its population characteristics in the Turkishregion, although some data about its reproductive andfeeding behavior are given by Çinar and Ergen (2005).

This paper presents the population and bio-ecologicalfeatures of Pseudonereis anomala collected fromdifferent habitats in ‹skenderun Bay (Levantine coast ofTurkey) in September 2005.

Material and Methods

A cruise to the Turkish Levantine coast wasundertaken in September 2005 to collect samples ofbenthos from different depths and habitats. In this studyonly samples taken from ‹skenderun Bay were evaluated.Scuba diving and snorkeling were used at 8 shallow waterstations (ca. 0-5 m; Figure 1). Specimens of Pseudonereisanomala were only found on algae [Ulva sp., Jania rubens(Linnaeus) Lamouroux, Cystoseira sp., Padina pavonica(Linnaeus) Thivy] on rocks, and among Brachidontespharaonis (P. Fischer, 1870) at depths of 0-3 m. At allstations samples were taken within a 20 × 20 cmquadrat.

In the laboratory the samples were sorted under astereomicroscope and specimens of Pseudonereisanomala were separated from other taxa, identified, andcounted. The body length and width at chaetiger 10(excluding parapodia) of unbroken specimens (n = 93)

A Preliminary Study on the Population Characteristics of the Lessepsian Species Pseudonereis anomala(Polychaeta: Nereididae) in ‹skenderun Bay (Levantine Sea, Eastern Mediterranean)

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Figure 1. Map of the study area and sampling site locations.

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were determined with an ocular micrometer. The wet-weight of specimens was estimated using a balancesensitive to 0.0001 g. All specimens measured weredissected to observe their gametes and gut contents.

To characterize population structures of Pseudonereisanomala in the area, regression and Pearson product-moment correlation analyses were performed on the dataset to assess the relationships among the biometricalmeasurements taken.

Results

In all, 434 specimens of Pseudonereis anomala werefound at 8 stations located in and around ‹skenderun Bay.

The mean density of Pseudonereis anomala at stationsvaried from 779 ind. m-2 (station K1) to 8 ind. m-2

(station K11), and the wet-weight biomass ranged from6 g m-2 (station K7) to 0.04 g m-2 (station K11 (Figure2). The maximum density and biomass values of P.anomala in ‹skenderun Bay were 2475 ind. m-2 (at stationK1, on Jania rubens) and 7.85 g m-2 (at station K5, onBrachidontes pharaonis), respectively.

The highest mean population density (550 ind. m-2) ofPseudonereis anomala was found on samples of theLessepsian mussel, Branchidontes pharaonis, whereassamples of the brown alga Padina pavonica contained onlya few individuals (Figure 3). The more structurallycomplex brown alga, Cystoseira sp., supported largeindividuals of P. anomala and the highest mean biomassscore of the species was encountered in this habitat(Figure 3).

The mean density and biomass values of Pseudonereisanomala on the mussel Brachidontes pharaonis variedaccording to station; 858 ind. m-2 and 3.83 g m-2 atstation K5, and 242 ind. m-2 and 1.83 g m-2 at stationK1.

A similar finding was noted with regard to the redalga Jania rubens. The population and biomass values ofPseudonereis anomala were higher on the alga samplescollected at station K1 and these values diminished at themore northern stations (Figure 4).

The individual body length of Pseudonereis anomala in‹skenderun Bay ranged from 0.2 to 27.3 mm (Figure 5);

M. E. ÇINAR, C. ALTUN

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Figure 2. Mean density and biomass values of Pseudonereis anomala at stations in ‹skenderunBay. Bar represents + standard error.


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Figure 3. Mean density and biomass values of Pseudonereis anomala in habitats in ‹skenderunBay. Bar represents + standard error.

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Figure 4. Mean density and biomass values of Pseudonereis anomala on the alga Jania rubens in‹skenderun Bay. Bar represents + standard error. The under-water photograph ofJ. rubens was taken at station 10 by Alp Can.

most commonly the length ranged between 5 and 10 mm(n = 34). The body width varied between 0.2 and 2.46mm, with individuals of 0.6-0.8 mm body width beingdominant (Figure 5). Although the individual biomass ofthe species varied from 2 to 35 mg in the area, 75% ofthe population had a biomass value between 2 and 5 mg,showing the importance of juvenile individuals in thepopulation (Figure 5).

The length (mm)-weight (mg) relationship ofPseudonereis anomala individuals is presented in Figure6. The regression formula for the relationship was W =0.0035 × L2.55, indicating that the growth of P. anomalais allometric, as the parameter b (2.55) was < 3.However, the regression equation estimated between thebody width and weight suggests that growth could alsobe isometric as the parameter b (2.95) approaches 3. Therelationship between the number of chaetigers and bodyweight was exponential (Figure 6). The body weightremains somewhat constant in specimens with 16-43chaetigers and suddenly increases in individuals havingmore than 43.

The relationship between body length and the numberof chaetigers of individuals of the species was logarithmicand the correlation score between these parameters wassignificantly high (r = 0.92, P < 0.05) (Figure 7). A linear


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Figure 5. The length, width, and weight frequency histograms of individuals of Pseudonereisanomala collected from ‹skenderun Bay in September 2005.

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Figure 6. The length-weight, width-weight, and chaetiger numbers-weight relationships of Pseudonereis anomala.

relationship was estimated between the body length andwidth (Figure 7).

The body weight, width, length, and chaetigernumber of Pseudonereis anomala samples collected fromthe alga (Jania rubens) and mussel (Branchidontespharaonis) did not differ significantly (t test, P < 0.05)

Among the specimens examined, only one specimenhad eggs in its coelomic cavity; egg mean diameter was67.9 µm ± 1.09 SE (n = 40) and minimum-maximumvalues were 50 and 85 µm. No clues (enlarged eyes,modified parapodia, and swimming chaetae) of epitokalmodifications were observed on the specimens.

Dissection of the digestive tracts of Pseudonereisanomala specimens collected in ‹skenderun Bay revealedthat they largely consumed algae and detritus. Pieces ofalgae, such as Padina pavonica, Cystoseira sp., and Janiarubens, were identified among the material gatheredfrom the digestive tracts of the specimens. In addition,some filamentous algae and sand were also found. Noresidue of animals was identified in the digestive tracts ofthe dissected specimens.

Discussion

In contrast to the alien serpulid species in theMediterranean, which have a negative economic impact,as they foul artificial substrates, such as docks, ship hulls,and sea-water intake pipes, alien nereidid species, such as

Pseudonereis anomala, could act as a potential foodsource for many large predators, including crabs andfishes. However, Ben-Eliahu (1989) reported thatPerinereis cultrifera (Grube, 1840), a native nereididspecies of the Mediterranean, was excluded from ashallow-water algal habitat along the Israeli coast,probably due to an inferior dispersal method; P. cultriferaappears to have direct, non-pelagic reproduction alongthe Levant coast and its dispersal is consequently morerestricted than that of the migrant species (Pseudonereisanomala), which have the Heteronereis stage and are ableto swarm in the open sea. However, Rouabah and Scaps(2003) found a dense population of Perinereis cultriferaoff the coast of Algeria reproducing exclusively by epitoky.Çinar and Ergen (2005) postulated that P. anomala has apotential to compete with other native species for spaceand food. However, the functioning role of this species inbenthic communities along the Mediterranean coast and itsimpact on the native fauna is largely unknown.

Pseudonereis anomala was previously found in avariety of shallow water benthic habitats (0-4 m), such ascorals, rocks, algae, mussels, and sand (Fishelson andRullier, 1969; Wu et al., 1985; Ergen and Çinar, 1997;Çinar and Ergen, 2005). Ben-Eliahu (1991) regarded thisspecies as an ecological generalist, a character suitable forsuccessful migrant species. Although P. anomala waspreviously reported from undisturbed environmentalconditions, Çinar and Ergen (2005) encountered it on themussel Mytilus galloprovincialis (Lamarck, 1819) inpolluted harbors in the Aegean Sea. The occurrence ofthis species in polluted waters was also confirmed byKambouroglou and Nicolaidou (2006) off the coast ofGreece. This shows that it has a wide ecological valancethat enables it to gradually extend its distributional rangefrom the eastern to the western Mediterranean.

The population of Pseudonereis anomala in‹skenderun Bay was mainly composed of juveniles,indicating that the reproduction period of the speciestook place in mid- or late summer. Only one specimencarried immature oocytes (oocyte diameter: 50-85 µm),without epitokal modifications. The diameter of matureoocytes in specimens with epitokal modification mayreach 195 µm (Çinar and Ergen, 2005).

The maximum body length (27.3 mm) ofPseudonereis anomala found in ‹skenderun Bay wassmaller than that of populations found in the Indian Ocean(65 mm) (Fauvel, 1953; Day, 1967), Red Sea (45 mm)


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Figure 7. The length-number of chaetigers and length-widthrelationships of Pseudonereis anomala.

(Fishelson and Rullier, 1969), and the Aegean Sea (51mm) (Çinar and Ergen, 2005). However, the samplingperiod of the present study took place soon after thereproduction of this species in ‹skenderun Bay (accordingto the number of juveniles in samples) and the largestspecimens might have died after reproducing. Therefore,the body size of the species in ‹skenderun Bay might belarger than what we measured. Ben-Eliahu (1989) foundthat large Mediterranean individuals of P. anomala livingon a Dendropoma habitat off the Israeli coast were largerthan the largest specimens of this species in a similarhabitat in the Red Sea. The difference in body sizesbetween the populations was thought to be, mostprobably, due to the colder Mediterranean temperature,the local stability of the Mediterranean Dendropoma reef,or a combination of these and other reasons (Ben-Eliahu,1989).

Data concerning the population density and biomassof Pseudonereis anomala are scarce. The populationdensity of this species is reported to be 47 ind. m-2 onDendropoma reefs along the Mediterranean coast ofIsrael and 15 ind. m-2 in a similar habitat of the Red Sea(Ben-Eliahu, 1989). Çinar and Ergen (1995) reported themaximum density and biomass scores of P. anomala in‹zmir Bay as 100 ind. m-2 and 4.08 g m-2. In ‹skenderunBay, the maximum density and biomass values of P.anomala were 2475 ind. m-2 (on Jania rubens at station1, mostly juvenile) and 7.85 g m-2 (on Brachidontespharonis at station 5). The highest mean density values ofP. anomala were encountered on the mussel B. pharonisand the brown alga Cystoseira sp. in ‹skenderun Bay.These habitats seem to have more complex structures forspecies settlement than others (J. rubens, Ulva sp., andPadina pavonica) sampled. Brachidontes pharonis formsdense populations on rocky substrates in the area andsediments trapped among shells and byssuses couldprovide more micro-habitats for the species. The thallusof Cystoseira sp. is more branched and larger than theother alga sampled, and so it could accumulate moresediment and thereby provide more food for speciespopulations. The thallus structure and availability ofnourishment on the host plant were reported to be major

factors affecting species diversity and density (Fishelsonand Haran, 1986/87; Çinar, 2003).

The body length-weight relationship of thePseudonereis anomala specimens may be indicative ofallometric growth; however, the b value (2.95) in theregression equation calculated between the body widthand weight of specimens of the species suggests isometricgrowth. This finding suggests that the width of theanterior segments increases proportionally to increasingbody weight, but the length of worms, increasing byadding new segments to the posterior part, represents anallometric relationship with body weight. A similar findingwas also noted by Omena and Amaral (2001), who foundthat the allometric coefficient obtained from the length ofthe prostomium to chaetiger 13 showed a close valuefrom an isometric growth (2.91). They explained that thelength of the anterior part of the worm increasesisometrically as the anterior region lengthens inproportion to weight and that this part of the body ismore important in the worm’s total weight than theposterior part. Allometric growth was also previouslydetermined in the nereidid Laeonereis acuta (Treadwell,1923; Omena and Amaral, 2001) and the tube wormDiopatra neapolitana Delle Chiaje, 1841 (Dagli et al.,2005).

The present study provides information about thepopulation characteristics of Pseudonereis anomala foundin ‹skenderun Bay in September 2005. Future studies tobe undertaken on the population structure and biology ofthis Lessepsian species throughout the year will shedmore light on its life history and functional role in theinvaded ecosystem.

Acknowledgments

We are obliged to our colleagues at the Department ofHydrobiology, Ege University, for their help in collectingand sorting the benthic materials and to 2 anonymousreferees for critically reading the manuscript. This workwas financially supported by TÜB‹TAK (Project Number:104Y065, coordinated by M.E. Çınar).


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Documents

A Preliminary Study on the Population Characteristics of ...journals.tubitak.gov.tr/zoology/issues/zoo-07-31-4/zoo-31-4-17-0611-15.pdf · (Levantin Denizi, Do¤u Akdeniz) Populasyon