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Primary settlement substrate of scallop, Zygochlamys patagonica (King and Broderip, 1832) (Mollusca: Pectinidae) in fishing grounds in the Argentine Sea.

ABSTRACT The Patagonian scallop (Zvgochlamys patagonica) fishery started in the Argentine Sea after exploratory cruises developed during 1995. Knowledge concerning the habitat requirements involved in the settlement processes of the target species was lacking. The main objectives of this study are to find Z. patagonica spat and to assess the characteristics and distribution of its primary settlement substrate (PSS). We observed under binocular microscope different invertebrate species (potential PSS) collected during 2006 from 125 sampling sites between 37[degrees] to 44[degrees]S and 83-133 m depth. Spat were found on the hydroid Symplectoscyphus subdichotomus (n = 215) and on adult Patagonian scallops (n = 51, attached to the encrusting sponge lophon proximum, amphipod, and polychaete tubes in nearly half of the cases). To analyze possible interactions between the benthic assemblage and scallop spat throughout the study area, we performed a faunal analysis including the species considered potential PSS (hydroids and scallops) and potential predators. The analysis showed a unique cluster of species closely associated, with variable abundance of hydroids (higher in samples with spat), scallops, and predators. A particular study in MDQ Area (38[degrees]S) shows that the sites where spat was collected presented lower density of potential predators and had been scarcely fished in comparison with the other sites within the area. The availability of PSS should be monitored and areas with dense patches of dichotomous hydroids should be protected from trawling.

KEY WORDS: scallop, spat, Zygochlamys patagonica, fishery, Argentine Sea

INTRODUCTION

Different processes are recognized to produce variability in the recruitment of benthic species with pelagic larval stages: production, dispersal, survival, settlement, growth, and survival of recently settled juveniles (Morgan 2001, Underwood & Keough 2001). For a benthic scallop, larval production will depend on adult stocks, the dispersal and survival in the plankton on oceanographic dynamics, and the settlement and post-settlement survival mainly on bottom characteristics and community structure to which settlers arrive (Pacheco & Stotz 2006). The settlement process is greatly dependent on the general architecture provided by the benthic environment, as propitious microhabitats are formed by the shells, shells litter, and biota. Settlement sites for scallop larvae provide refuges from predation, reduce physical stress, and influence the transport of particles to the benthic habitat (Gutierrez et al. 2003, Guay & Himmelman 2004). The most preferred primary settlement substrate (PSS) for scallop species are filamentous, such as algae, seagrasses, and colonial groups like bryozoans and hydroids; stones, empty shells, and adult scallops are also reported among natural settlement substrates (see Cragg 2006 for a review).

The availability of settlement sites may limit larval settlement and consequently affect recruitment, even when larvae are abundant (Morgan 2001). The knowledge of settlement processes of exploited species is of practical importance to better understand the dynamics of the stocks and avoid overexploitation (Aguilar & Stotz 2000). In this context, considering also that trawling can impact the bottom in many ways (i.e., Lindeboom & de Groot 1998, Collie et al. 2002, Bradshaw et al. 2002, Kenchington et al. 2007), knowledge concerning the PSS of the benthic resources is needed as a first step to know the habitat requirements of the target species. This kind of information was lacking in relation with the Patagonian scallop, widely distributed and exploited in the Argentine Sea. Consequently, we dealt with our main objective to find Zygochlamys' patagonica spat and to assess the characteristics and distribution of the primary settlement substrate--and present our findings in this paper. The results gain importance in the fisheries context, by means of providing a management tool in relation with the establishment of no-take areas.

The Patagonian scallop fishery started after exploratory cruises during 1995 (Lasta & Bremec 1998); produced total annual scallop catches ranging from 37,000 to nearly 43,000 tons/year between 1996 and 2005. Evaluation of the different management sectors is developed annually to assess biomass of the stocks (specimens from 4-5 mm shell height) and composition of the invertebrate by-catch. During 2006, according to our objective, we faced the study of epibiosis on invertebrates with particular emphasis to register the presence of recently settled spat (sensu Cragg 2006) of Z. patagonica and to recognize the PSS in the exploited areas along the highly productive shelf break front (Acha et al. 2004). Our sampling conducted to the present results about spatial distribution of microscopic spat and preferential PSS between 37[degrees] and 44[degrees]S along the 100-m isobath in the Argentine Sea.

MATERIALS AND METHODS

Specimens of different invertebrate species were observed under binocular microscope to assess the presence of patagonian scallop recently settled spat. Benthic fauna was collected during the evaluation cruises carried out in the two management sectors (CC 05/06 and CC 06/06 INIDEP respectively); 85 stations were sampled in a Northern Sector (March 30 to April 10, 2006; Areas North, MDQ and Reclutas) between 37[degrees]00'S 39[degrees]30'S and 83-128 m depth and 40 stations were sampled in a southern sector (May 29 to June 7, 2006; Areas San Bias, SAO, SWSAO, Valdes, Tango B, SW Tango B and FUS) between 39[degrees]34'S-43[degrees]53'S and 87-133 m depth (Fig. 1). The sampling procedure was designed for evaluation of Z. patagonica purposes and the total number of sampling sites in the different areas is, in most of the cases, in accordance with their area in [km.sup.2] (Lasta et al. 2006a, Lasta et al. 2006b). We focused our study in those species that offer filamentous surfaces and we examined all the material obtained in the following cases: Fusitriton m. magellanicus (snail), Symplectoscyphus subdichotomus, Grammaria magellanica (hydroids), and Bryozoa unidentified. We also sampled living scallops (nearly 10 individuals per location) higher than 45 mm (commercial size [greater than or equal to] 55 mm). In addition, we observed a few specimens of other snails (Odontocymbiola magellanica and Adelomelon ancilla), polychaete tubes (Phy11ochaetopterus socialis and Idanthyrsus armatus), echinoderms (Pseudechinus magellanicus and Gorgonocephalus chilensis), and Patagonian scallop shells. The total number or weight (g) of the material analyzed is shown in Table 1. Spat length ([micro]m) was measured under binocular microscope and the size distribution data between substrata and sectors were compared by Mann-Whitney rank sum test.

To analyze the general composition of the benthic assemblage potentially interacting with scallop spat throughout the study area, we performed a faunal analysis considering potential substrata (scallops and total hydroids) and potential predators (see Botto et al. 2006), from the total number of samples analyzed in both management sectors. Species were sorted, identified, counted, and weighed in the laboratory. Cluster analysis was applied to presence-absence data (Sorensen index) and to fourth-root transformed abundance data (BrayCurtis index) (UPGMA, R mode) (Clarke & Warwick 1993). The SIMPER test (Clarke 1993) was used to identify which species contributed most to the similarity (up to 90%) between samples without spat, with spat on scallops, and with spat on hydroids.

[FIGURE 1 OMITTED]

A local assessment of density of potential substrata and predators was conducted in MDQ bed, where higher abundance of spat was found during this study. For resource evaluation purposes, this bed is divided in different areas (67 [km.sup.2] each). We considered densities in the following four areas: whole bed (MDQ, 44 samples), areas where spat was found (herein named MDQ box, 13 samples), in the rest of the areas adjacent to MDQ box (MDQ adj., 31 samples) and in the samples from MDQ box that presented spat (MDQ spat, 4 samples). The densities between MDQ box and MDQ adj. were compared with t-test (normal distribution of data in the case of scallops and predators) and Mann-Whitney rank sum test (hydroids). Data were transformed ([log.sub.10][x + 1]) prior to analysis.

RESULTS

Zygochlamys patagonica recently settled spat were found on the hydroid Symplectoscyphus subdichotomus (n = 215) and on Patagonian scallops (n = 51) in the study area during 2006; only one spat was observed on a scallop shell (Table 1). In the case of living scallops, 25 spat were settled on epibionts of their valves (the sponge lophon proximum (Fig. 2), amphipod tubes and polychaete tubes). We observed a total of 1,278 scallops from 125 sampling sites (100% of total sites with scallops) and we found 51 spat on 48 scallops from 25 sites. The hydroid S. subdichotomus was present in 86 from 125 sites, and we observed 679 g from 47 sites (55% of the total sites with hydroids). We found 215 spat in 175 g of hydroid from 10 sites (Table 1 ; Fig. 3).

[FIGURE 2 OMITTED]

This preferential settlement on hydroids was found in both management sectors. In the Northern Sector (North, MDQ, Reclutas), we observed 880 adult scallops from 85 sampling sites and we found 49 spat (average size 1,136.11 [micro]m: range 6243,504 [micro]m) on 46 living scallops (average shell length 61.6 mm) in 23 sites. The maximum number of spat on scallops was 2. In this sector, we analyzed 273 g of S. subdichotomus from 21 sites and we found 183 spat (average size 1,116.33 [micro]m; range 480-2,304 [micro]m) in 106 g of hydroid from 5 sampling sites. Larger numbers, 14-86 spat, were found in 4 samples located between 38[degrees]13'S and 38[degrees]37'S in "MDQ box" at 91-95 m depth; in 3 of those samples spat were found on scallops and hydroids. Only one spat was found in the rest of the positive stations. The size distribution of spat was not significantly different between substrata (T = 5,244; P = 0.402).

In the Southern Sector (San Bias, SAO, SWSAO, Valdes, TangoB, SW TangoB, FUS) we observed 398 scallops from 40 sampling sites and we found 2 spat (816 [micro]m and 1,296 [micro]m) on 2 scallops (shell height 62 mm) in 2 sites. In this sector, we observed 405 g of S. subdichotomus from 26 sites and we found 32 spat (average size 1,384.81 [micro]m; range 816-3,654 [micro]m) in 69.2 g of hydroid from 6 sampling sites. The presence of spat in the southern sector was registered along its latitudinal range; the higher value (n = 19) at 42[degrees]19'S, 117 m depth (Area Valdes), followed by 5-6 spat in other two sampling stations. Only 1-2 spat were found at the remaining stations and only in one station (SWTango B) spat on hydroid and scallop was found. The size distribution of spat was not significantly different between substrata (T = 80.5; P = 0.15).

[FIGURE 3 OMITTED]

The size distribution of spat between Sectors was different (T = 6,487; P = 0.001), with higher sizes sampled in the Southern Sector between March 29 to June 7 (median = 1,248 [micro]m) than in the northern one between March 30 to April 10 (median = 1.056 [micro]m).

The spatial distribution of potential settlement substrata of Patagonian scallops spat in the study area during 2006 is shown in Figure 4. Both hydroids and scallops >55 mm (commercial size) were distributed all along the commercially exploited zone. Densities of hydroids were in general <0.6 g [m.sup.-2] in sampling sites from all the distributional range, and higher in some locations mainly from the southern zone. Scallops >55 mm were more abundant (>5 ind. [m.sup.-2]) in northern areas.

[FIGURE 4 OMITTED]

The cluster analysis (Fig. 5) shows that scallops and hydroids are closely associated (ca. 70% and 50% similarity with presence-absence and biomass data respectively) to a group of predator species identified in the benthic assemblage that characterizes the large study area between 37[degrees] to 44[degrees]S. These species are Austrocidaris canaliculata, Sterechinus agassizi, Calyptraster sp., Cosmasterias lurida, Ctenodiscus australis (echinoderms), Libidoclaea granaria (crustacean), and Fusitriton m. magellanicus (gastropod). The results of the SIMPER test performed to compare the faunal assemblages from stations without spat and with spat on different substrata are showed in Table 2. Hydrozoa present higher average abundance and contributions to similarity in the selected group of samples with spat in both management sectors. In the northern one, the lower abundance of scallops and potential predators is conspicuous in the group of five samples with spat on hydroids. In the southern sector, a general lower abundance of scallops and predators, together with higher density of ophiuroids, in comparison with the other sector.

The abundance of predators and potential substrata was analyzed in detail for Area MDQ (Fig. 6). The average densities of hydroids were not significantly different between MDQ box and MDQ adj. (T = 306.0; P = 0.738). On the contrary, statistically significant differences between the same areas were estimated for densities of predators (t = 3.369; P - 0.002) and scallops (t = 2.116; P = 0.040). Although we did not consider MDQ spat in this analysis because of the low number of samples (n = 4), a higher average biomass of hydroids [m.sup.-2] in these stations is observed in Figure 6.

DISCUSSION AND CONCLUSION

Our sampling in the Z. patagonica grounds during 2006 successfully conducted to the recognition of recently settled spat and the PSS. Spat were found at different latitudes in the extensive study area (37[degrees]S to 44[degrees]S), on the living hydroid Symplectoscyphus subdichotomus and adults of the same scallop species. The absence of juveniles on scallop shells was previously mentioned from samples collected during 2001 (Bremec & Schejter 2005).

Symplectoscyphus subdichotomus is part of a hydroid assemblage characteristic of the scallop beds in the Argentine Sea, that includes 18 hydroid species settled on polychaete tubes, sponges, Patagonian scallops and other hydroid colonies, which conform the main biological substrata (Genzano et al., manuscript submitted). Recently-settled pectinid spat have been collected from many natural substrates; filamentous fauna and flora are in general some of the preferred substrata for settlement (see Cragg 2006 and references). We sorted all the hydroids from the samples and the more abundant were S. subdichotomus and Grammaria magellanica; we only found spat on the former species. G. magellanica colonies are more or less pinnate with a slightly branched and thick main stem instead; S. subdichotomus colonies have numerous side-branches arranged along a thin stem bent in zig-zag fashion or pseudodichotomously branched. The heterogeneous morphology of colony of this sertularid can be considered optimal for the settlement of scallop spat, in accordance with the hypothesis that proposes a passive deposition of larvae as a result from interactions between flow in the benthic boundary layer and the threedimensional heterogeneity (branching pattern) of filamentous structures (Harvey et al. 1993, 1995). Filamentous organisms, particularly hydroids, play an important role as settlement substrate for juvenile scallops, for instance Placopecten magellanicus in the Gulf of St. Lawrence (Stokesbury & Himmelman 1995) and Pecten maximus and Aequipecten opercularis in the Irish Sea (Bradshaw et al. 2003). Active processes at scales of 1.0 cm or less should involve a presumably benthic, behavioral response, consisting of migration on the substrata until a heterogeneous region is observed (Bourget & Harvey 1998).

Spat settled on Patagonian scallops were scarcely found all along the study area, no more than 2 spat per adult scallop, attached to the encrusting sponge Iophon proximum, amphipod, or polychaete tubes in nearly half of the cases. In this condition, the microhabitat should not protect the newly settled individuals from silting on bottom sediments, as occurs when scallop larvae prefer to settle on filamentous epibenthic substrata (see Pearce et al. 2004) and are better positioned for feeding on suspended particles. In this investigation we only considered scallops higher than 45 mm shell height to assess any degree of overspatting and to explore if spat could be caught together with commercial sizes. As these are sorted and retained by passing through a wet rotatory machine and processed onboard to obtain and freeze the muscles (Bremec et al. 2004), the implications of a restricted overspatting could be negative to the species dynamics.

[FIGURE 5 OMITTED]

The size structure of the target species is currently assessed from 4-5 mm shell height individuals (Campodonico & Lasta 2006, Marecos & Lasta 2006), mainly observed on living scallops when attached to any substrate. Scallops up to 35 mm height were observed settled on larger individuals (Bremec et al. 2003). The presence of juveniles on adult scallops could be the result of both primary and secondary settlement from another substrate, hydroids in this case. The detachment of juvenile scallops from the primary settlement substrate and posterior swimming or crawling short distances was described as a redispersion strategy to migrate to adult beds (Arsenault et al. 2000, Brand 2006).

Early studies on shell ontogeny of the species were developed on specimens of 5 mm minimum height size also collected in the Argentine Sea (Waloszek 1984). We found settled spat between the period March 30 to June 7 (austral autumn), with significantly different size distribution in different periods but without significant differences between substrates in both management sectors. The annual reproductive cycle of Z. patagonica, studied at area Reclutas, involved gametogenesis during austral autumn-winter and spawning with partial emissions during austral spring-summer months (Campodonico et al. in press). Zygochlamys patagonica fits well with the planktotrophic larvae theoretical model (PI/PII ratio of spat = 0.364 [+ or -] 0.025) and follows the general trend of planktotrophic larvae in the "size at metamorphosis versus temperature" Cragg's (2006) regression, considering a temperature of 6.5[degrees]C (Schejter & Bremec 2007, Schejter et al. 2007). Our data on range sizes of spat seem to support the described pattern of protracted spawning events and suggest that spat grew during the period April to June. These results add preliminary information related with the recruitment of the species in exploited areas, not enough to suggest any period of larval life.

Temperature is a major factor determining the overall geographical range of a scallop species, and the spatial and temporal stability of scallop populations will be dependent on the nature and stability of the hydrographic regimen, as spawning and larval retention and survival depend on large geographic scale conditions (Brand 2006, Orensanz et al. 2006). The large aggregations of Z. patagonica in areas coinciding with the boundary of the summer thermocline were early reported by Waloszek (1991), which could be explained by increased larval settlement at the intersection of thermoclines and the sea floor (Pearce et al. 1996, Pearce et al. 2004). The larger scale factors interact with smaller scale processes, including factors such as adequate substrate, food availability, the occurrence of competitors, and predators in determining the local distribution (Constable 1999, Brand 2006, Hart 2006, Orensanz et al. 2006). The spatial distribution of this factors related with the availability of suitable benthic habitat could affect postlarval growth and survival (Thouzeau 1991, Stokesbury & Himmelman 1995, Brown 1998).

The spatial distribution of the analyzed potential substrates covers the whole exploited area. Although our results show that hydroids, and in particular S. subdichotomus, can offer important primary settlement substrate to the target species, spat on hydroids were not distributed all over the spatial range analyzed. We characterized the benthic assemblage associated with Patagonian scallops at a large scale of ca. 8,000 [km.sup.2] (Lasta et al. 2006a, Lasta et al. 2006b) (grounds, following Brand 2006), considering the presence of potential substrates and predators (Botto et al. 2006). Our analysis shows a unique cluster of species closely associated throughout the study area, with variable average abundance of hydroids (higher in samples with spat), scallops, and predators in the groups of samples from both management sectors clustered for SIMPER test. The consistence of species composition over space and time was previously reported (Bremec & Lasta 2002). Although our sampling procedure was not designed to assess spat density, it is noticeable that higher numbers of spat (219 from a total of 266) on both substrates were obtained in Area MDQ (2871 [km.sup.2], Lasta et al. 2006a). This particular study shows that the areas where spat was collected presented lower density of potential predators and scallops, significantly different from the rest of the Area, and the density of hydroids was higher, regardless of the lack of significance in our estimations. Not surprisingly, 3 of the 4 samples with scallop spat come from an area with relative low density of commercial scallops and scarcely fished between January 1996 and August 1998 (M. Lasta pets. comm.).

[FIGURE 6 OMITTED]

Bottom fishing, in general, reduces habitat complexity by impacting sessile epifaunal species and associated fauna (Collie et al. 1997, Jennings & Kaiser 1998, Kaiser et al. 2000, Bremec et al. 2000, Kenchington et al. 2007). This sampling was conducted during 2006, after 10 y of commercial fishing of Z. patagonica in the Argentine Sea. We mainly found spat in sites within areas where exploitation was scarce and with higher abundance of hydroids (sessile epifauna). The reduction of settlement or juveniles survival in bottoms perturbed by fishing was suggested decades ago by Caddy (1973) and, as a general conclusion, the presence of substrate is related with the spatial variability of the recruitment, whereas variability between years is mainly the consequence of larval supply (see Fetzer 2005, Pacheco & Stotz 2006). We support the idea leading to the conservation of habitats that provide primary settlement substrate for spat as a first step to enforce successful recruitments, as both irregular recruitment and overfishing are mostly related to wide temporal fluctuations in scallop landings from important areas (see Orensanz et al. 1991). Still considering that large scale oceanographic processes could influence natural larvae settlement to the benthos at the intersection of thermoclines and the sea floor, that adult aggregations may be influenced by postsettlement migration, which should not occur at the scale of kilometres, and that high spat settlement does not explain where scallop beds become established (Brand 1991, Brand 2006, Stokesbury & Himmelman 1995), the availability of PSS should be monitored and areas with dense clumps of branched hydropolyps, and possibly lower abundance of predators, protected from trawling along the extensive area where fishing grounds are distributed.

ACKNOWLEDGMENTS

This paper was partially funded by PICT 1-15080, PIP 5009, Antorchas 13900-13, EXA 372/07 and PICT 1553. This is INIDEP Contribution No 1489. The authors specially thank Diego Giberto for his kind help.

LITERATURE CITED

Acha, E. M., H. Mianzan, R. Guerrero, M. Favero & J. Bava. 2004. Marine fronts at the continental shelves of austral South America. Physical and ecological processes. J. Mar. Syst. 44:83-105.

Aguilar, M. & W. Stotz. 2000. Settlement sites of juvenile scallops Argopecten purpuratus (Lamarck, 1819) in the subtidal zone at Puerto Aldea, Tongoy Bay, Chile. J. Shellfish Res. 19:749-755.

Arsenault, D. J., M. C. Giasson & J. H. Himmelman. 2000. Field examination of dispersion patterns of juvenile Iceland scallops (Chlamys islandica) in the northern Gulf of St. Lawrence. J. Mar. Biol. Assoc. UK. 80:501-508.

Botto, F., C. Bremec, A. Marecos, L. Schejter, M. Lasta & O. Iribarne. 2006. Identifying predators of the SW Atlantic Patagonian scallop Zygochlamys patagonica using stable isotopes. Fish. Res. 81:45-50.

Bourget, E. & M. Harvey. 1998. Spatial analysis of recruitment of marine invertebrates on arborescent substrata. Bigfouling 12:45-53.

Bradshaw, C., L. O. Veale & A. R. Brand. 2002. The role of scallop-dredge disturbance in long-term changes in Irish Sea benthic communities: a re-analysis of an historical dataset. J. Sea Res. 47:161-184.

Bradshaw, C., P. Collins & A. R. Brand. 2003. To what extent does upright sessile epifauna affect benthic biodiversity and community composition? Mar. Biol. 143:783-791.

Brand, A. R. 1991. Scallop ecology: distributions and behaviour. In: S. Shumway, editor. Scallops: biology, ecology and aquaculture. Amsterdam: Elsevier. pp. 517-584.

Brand, A. R. 2006. Scallop ecology: distributions and behaviour. In: S. Shumway & G. J. Parsons, editors. Scallops: biology, ecology and aquaculture, 2nd ed. Amsterdam: Elsevier. pp. 651-744.

Bremec, C. & M. L. Lasta. 2002. Epibenthic assemblage associated with scallop (Zygochlumys patagonica) beds in the Argentine shelf. Bull. Mar. Sci. 70:89-105.

Bremec, C. & L. Schejter. 2005. Latitudinal gradient of the patagonian scallop (Zygochlamys patagoniea) assemblage. Book of abstracts 15th International Pectinid Workshop, Moololaba, Australia. 90a-90c.

Bremec, C., T. Brey, M. Lasta, J. Valero & L. Lucifora. 2000. Zygochlamys patagonica beds on the Argentinean shelf. Part I: Energy flow through the scallop bed community. Arch. Fish. Mar. Res. 48:295-303.

Bremec, C., A. Marecos, L. Schejter & M. Lasta. 2003. Guia tecnica para la identificacidn de invertebrados epibentonicos asociados a bancos de vieira patagonica (Zygochlamys patagonica) en el Mar Argentino. Publicacion Especial INIDEP, Mar del Plata. 28 pp.

Bremec, C., M. L. Lasta & D. Hernandez. 2004. Survival of Patagonian scallop (Zygochlamys patagonica King and Broderip, 1832) after the size selection process on commercial fishing vessels. Fish. Res. 66:49-52.

Brown, D. W. 1998. Habitat essential for sustainable fisheries. J. Shellfish Res. 17:1481-1482.

Caddy, J. F. 1973. Underwater observations on tracks of dredges and trawls and some effects of dredging on a scallop ground. J. Fish. Res. Bd. Can. 30:173-180.

Campodonico, S. & M. Lasta. 2006. informe de Campana CC-06-06. Evaluacion de biomasa de vieira patagonica: Sector Sur. Bancos San Blas, SWSAO, Valdes, Tango B y SW Tango B. INIDEP Tech. Rep. 18:1-43.

Campodonico, S., G. Macchi, B. Lomovasky & M. Lasta. Reproductive cycle of the patagonian scallop Zygochlamys patagonica in the SW Atlantic. JMBA UK. (in press).

Clarke, K. R. 1993. Non-parametric multivariate analyses of changes in community structure. Aust. J. Ecol. 18:117-143.

Clarke, K. R. & R. Warwick. 1993. Environmental effects on benthic communities. Training Workshop on "Multivariate Analysis of Benthic Community Data." Lecture notes for SEAS/EPOSII Workshop, Plymouth Marine Laboratory. 144 pp.

Collie, J., A. E. Galo & P. C. Valentine. 1997. Effects of bottom fishing on the benthic megafauna of Georges Bank. Mar. Ecol. Prog. Ser. 155:159-172.

Collie, J., S. Hall, M. Kaiser & I. R. Poiner. 2002. A quantitative analysis of fishing impacts on shelf-sea benthos. J. Ecol. 69:785-798.

Constable, A. J. 1999. Ecology of benthic macro-invertebrates in soft-sediment environments: A review of progress towards quantitative models and predictions. Aust. J. Ecol. 24:452-476.

Cragg, S. 2006. Development, physiology, behaviour and ecology of scallop larvae. In: S. Shumway & G. J. Parsons, editors. Scallops: biology, ecology and aquaculture. 2nd ed. Elsevier, Amsterdam. pp. 45-105.

Fetzer, I. 2005. Reproduction strategies and distribution of larvae and juveniles of benthic soft-bottom invertebrates in the Kara Sea (Russian Arctic). Ber Polarforsch Meeresforsch 496. 200 pp.

Genzano, G., D. Giberto, L. Schejter, C. Bremec & P. Meretta. Hydroid from SW Atlantic (34[degrees]-43[degrees]S): richness and assemblages. Mar. Ecol. PSZN (submitted).

Gutierrez, J. L., C. G. Jones, D. L. Strayer & O. O. Iribarne. 2003. Mollusks as ecosystem engineers: the role of shell production in aquatic habitats. Oikos 101:79-90.

Guay, M. & J. H. Himmelman. 2004. Would adding scallop shells (Chlamys islandica) to the sea bottom enhance recruitment of commercial species? J. Exp. Mar. Biol. Ecol. 312:299-317.

Hart, D. 2006. Effects of sea stars and crabs on sea scallop Placopecten magellanicus recruitment in the Mid-Atlantic Bight (USA). Mar. Ecol. Prog. Ser. 306:209-221.

Harvey, M., E. Bourget & R. G. Ingrain. 1995. Experimental evidence of passive accumulation of marine bivalve larvae on filamentous epibenthic structure. Limnol. Oceanog. 40:94-104.

Harvey, M., E. Bourget & G. Miron. 1993. Settlement of Iceland scallop Chlamys islandica spat in response to hydroids and filamentous red algae: field observations and laboratory experiments. Mar. Ecol. Prog. Set. 99:283-292.

Jennings, S. & M. J. Kaiser. 1998. The effects of fishing on marine ecosystems. Adv. Mar. Biol. 34:201-351.

Kaiser, M. J., K. Ramsay, C. A. Richardson, F. E. Spence & A. R. Brand. 2000. Chronic fishing disturbance has changed shelf sea benthic community structure. J. Ecol. 69:494-503.

Kenchington, E. L., T. Kenchington, L. A. Henry, S. Fuller & P. Gonzalez. 2007. Multi-decadal changes in the megabenthos of the Bay of Fundy: The effects of fishing. J. Sea Res. 58:220-240.

Lasta, M. & C. Bremec. 1998. Zygochlamys patagonica in the Argentine Sea: a new scallop fishery. J. Shellfish Res. 17:103-111.

Lasta, M., D. Hernandez & S. Campodonico. 2006a. Vieira Patagonica Sector Norte. Evaluacion de biomasa ano 2006. INIDEP Techn. Rep. 69:1-21.

Lasta, M., D. Hernandez & S. Campodonico. 2006b. Vieira Patagonica Sector Sur. Evaluacion de biomasa ano 2006. INIDEP Techn. Rep. 42:1-13.

Lindeboom, H. J. & S. J. de Groot. 1998. Impact-II. The effects of different types of fisheries on the North Sea and Irish Sea benthic ecosystems. NIOZ- Rapport 1998-1, RIVO-DLO Report C003/98. 404 pp.

Marecos, A. & M. Lasta. 2006. Informe de Campana CC-05-06. Evaluacion de biomasa de vieira patagonica. Sector Norte de Manejo: Bancos Reclutas, MDQ y Area "a". INIDEP Tech. Rep. 15:1-51.

Morgan, S. G. 2001. The larval ecology of marine communities. In: M. D. Bertness, S. D. Gaines & M. E. Hay, editors. Marine community ecology. Sunderland, Massachusetts: Sinauer Associates, Inc. pp. 159-181.

Orensanz, J. M., A. M. Parma & O. O. Iribarne. 1991. Population dynamics and management of natural stocks. In: S. E. Shumway, editor. Scallops: biology, ecology and aquaculture. Amsterdam: Elsevier. pp. 625-713.

Orensanz, J. M. (Lobo), A. M. Parma, T. Turk & J. Valero. 2006. Dynamics, assessment and management of exploited natural populations. In: S. Shumway & G. J. Parsons, editors. Scallops: biology, ecology and aquaculture. 2nd ed. Amsterdam: Elsevier. pp. 765-868.

Pacheco, A. & W. Stotz. 2006. Will providing a filamentous substratum in the water column and shell litter on the bottom increase settlement and post-larval survival of the scallop A. purpuratus? J. Exp. Mar. Biol. Ecol. 333:27-39.

Pearce, C. M., S. M. Gallager, J. L. Manuel, D. A. Manning, R. K. O'Dor & E. Bourget. 1996. Settlement of larvae of the giant scallop, Placopecten magellanicus, in 9-m deep mesocosms as a function of temperature stratification, depth, food and substratum. Mar. Biol. 124:693-706.

Pearce, C. M., J. L. Manuel, S. M. Gallager, D. A. Manning, R. K. O'Dor & E. Bourget. 2004. Depth and timing of settlement of veligers from different populations of giant scallop, Placopecten magellamicus (Gmelin), in thermally stratified mesocosms. J. Exp. Mar. Biol. Ecol. 312:187-214.

Schejter, L. & C. Bremec. 2007. Did the epibenthic bycatch at the Patagonian scallop assemblage change after ten years of fishing'? Book of abstracts 16th International Pectinid Workshop, Halifax, Canada: 102-104.

Schejter, L., C. Bremec & D. Waloszek. 2007. Empirical evidence of planktotrophic life in Zygochlamys patagonica larvae. 16th Int. Pectinid Workshop, Halifax, Canada, May 11-18, Book of abstracts, pp. 183-185.

Stokesbury, K. D. E. & J. Himmelman. 1995. Biological and physical variables associated with aggregations of the giant scallop Placopecten magellanicus. Can. J. Fish. Aquat. Sci. 52:743-753.

Thouzeau, G. 1991. Experimental collection of postlarvae of Pecten maximus (L.) and other benthic macrofaunal species in the Bay of Saint-Brieue, France. I. settlement patterns and biotic interactions among the species collected. J. Exp. Mar. Biol. Ecol. 148:159-179.

Waloszek, D. 1984. Variabilitat, Taxonomie und Verbreitung yon Chlmays patagonica (King & Broderip, 1832) und Anmerkungen zu weiteren Chlmays- Arten (Mollusca, Bivalvia, Pectinidae). Verh Naturwiss Ver Hamburg 27:207-276.

Waloszek, D. 1991. Chlamys patagonica (King & Broderip, 1832), a long "neglected" species from the shelf off the Patagonia Coast. In: P. A. Sandifer, editor. World Aquaculture Workshops, Number 1, An International Compendium of Scallop Biology and Culture, Baton Rouge, Louisinana. pp 256-263.

Underwood, A. J. & M. J. Keough. 2001. Supply-side ecology. The nature and consequences of variations in recruitment of intertidal organisms. In: M. D. Bertness, S. D. Gaines & M. E. Hay, editors. Marine community ecology. Sunderland, Massachusetts: Sinauer Associates, Inc. pp 183-200.

CLAUDIA BREMEC, (1,2) * MARIANA ESCOLAR, (2,3) LAURA SCHEJTER (1,2) AND GABRIEL GENZANO (1,4)

(1) Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET). Rivadavia 1917, C1033AAJ Buenos Aires, Argentina; (2) Instituto Nacional de Investigacion y Desarrollo Pesquero (INIDEP). V. Ocampo 1, 7600 Mar del Plata, Argentina, P.O. Box 175; (3) Agencia Nacional Promocion Cientifica y Tecnologica (ANPCyT). Cordoba 831 - 6[degrees] piso 1054AAH Buenos Aires, Argentina; (4) Departamento de Ciencias Marinas. Facultad de Ciencias Exactas y Naturales. Universidad Nacional de Mar del Plata, Funes 3350, Mar del Plata, Argentina

* Corresponding author. E-mail: cbremec@inidep.edu.ar
TABLE 1.
List of substrata analyzed and number of spat registered
in this study.
 No.
 Sample Scallop
Substrate Size Spat

Symplectoscyphus subdichotomus * 679 215
Grammaria magellanica * 18.24 0
Zygochlamys patagonica ** 1278 51
Fusitriton magellanicus ** 173 0
Adelomelon ancilla ** 3 0
Odontocymbiola magallanica ** 2 0
Volutidae 2 0
Pseudechinus magellanicus ** 2 0
Gorgonocephalus chilensis ** 2 0
Tubes Phyllochaetopterus socialis * 48.55 0
Tubes ldanthyrsus armatus * 56.33 0
Bryozoa indet. 27.19 0
Zygochlamys patagonica shells * 461.79 1

* Wet weight in grams. ** No individuals.

TABLE 2.
Average abundance (g [m.sup.-2]) and contribution to similarity (%)
in the groups of stations without spat, with spat on adult scallops
and with spat on hydroids, in both management sectors sampled
during 2006 in the Argentine Sea. The number of stations, number
of spat in the different substrata and average similarity of
each group of stations is indicated.

 Northern Management Sector

No. stations 60 23 5

Substrate (No. spat) No spat Z. S.
 patagonica subdichotomus
 (49 in (l83 in
 46 ind.) 106 g)

Average similarity 51.93 48.03 63.15

TAXA Average abundance (g [m.sup.-2])/
 Contribution to similarity 90%
PORIFERA
 Tedania spp. 3.69/5.00 1.92/4.81 0.29/4.86

CNIDARIA
 Hydrozoa colonies -- 0.18 /1.37 0.37/4.28
 Actinostola
 crassicornis -- -- --
 Alcyonium digitatum 0.59/4.37 0.16/4.91 0.09/3.18
 Flabellum sp. 0.58/2.89 0.36/3.64 --

POLYCHAETA
 Chaetopterus
 variopedatus
 (tubes) 4.29/3.04 2.76/4.07 0.23/4.49
 Idanthyrsus
 armatus (tubes) 6.60/3.68 0.83/2.87 0.71/4.92

GASTROPODA
 Adelomelon ancilla 1.66/1.54 2.76/1.59 2.09/2.73
 Fusitriton m.
 magellanicus 2.80/3.54 1.75/3,94 0.86/5.70

BIVALVIA
 Zygochlamys
 patagonica 66.33/15.19 60.88/22.48 25.55 /l2.40

MALACOSTRACA
 Serolis schytei -- -- --
 Eurypodius latreillei 0.15/1.10 -- --
 Libidoclaea granaria 0.55/4.09 0.43/5.53 0.20/4.52

HOLOTHUROIDEA
 Psolus patagonicus 0.13/2.14 0.09/2.88 --
 Pseudocnus
 dubiosus leoninus 0.13/2.15 -- 0.01/1.32

ECHINOIDEA
 Austrocidaris
 canaliculata 1.21/4.99 0.53/2.22 0.48/3.31
 Sterechinus agassizi 1.17/1.67 0.18/0.90 0.08/1.28

ASTEROIDEA
 Calvptraster sp. 0.95/3.87 0.77/4.14 0.30/5.24
 Cosmasterias lurida 1.76/5.80 0.51/3.61 0.50/5.37
 Ctenodiscus australis 1.80/6.40 0.87/6.24 0.40/3.44
 Labidiaster sp. 3.02/1.45 6.46/2.52 1.62/4.96

OPHIUROIDEA
 Gorgonocephalus
 chilensis 3.27/3.81 1.56/4.97 1.49/7.81
 Ophiacanta vivopara 2.86/2.59 1.26/1.74 --
 Ophiactis aspeula 1.62/4.65 1.25/4.50 0.57/3.20
 Ophiuroglypha lymanii 1.55/1.53 -- --

 Southern Management Sector

No. stations 33 2 6

Substrate (No. spat) No spat Z. S.
 patagonica subdichotomus
 (2 in 2 ind.) (32 in 69 g)

Average similarity 54.80 58.61 57.32

TAXA Average abundance (g [m.sup.-2])/
 Contribution to similarity 90%
PORIFERA
 Tedania spp. 2.52/6.22 4.99/8.64 3.45/4.68

CNIDARIA
 Hydrozoa colonies 0.60/3.16 0.21/4.33 1.20/6.73
 Actinostola
 crassicornis 0.82/1.58 -- --
 Alcyonium digitatuin 0.31/5.07 0.05/3.32 0.30/4.60
 Flabellum sp. -- -- --

POLYCHAETA
 Chaetopterus
 variopedatus
 (tubes) 0.36/1.69 -- --
 Idanthyrsus
 armatus (tubes) 1.21/2.56 -- 0.64/5.28

GASTROPODA
 Adelomelon ancilla 1.84/1.45 2.60/7.92 --
 Fusitriton m.
 magellanicus 0.61/1.85 -- 1.34/2.40

BIVALVIA
 Zygochlamys
 patagonica 38.60/17.61 24.69/12.75 37.55/17.00

MALACOSTRACA
 Serolis schytei 0.09/1.73 0.24/3.20 0.23/1.95
 Eurypodius latreillei -- -- --
 Libidoclaea granaria -- -- --

HOLOTHUROIDEA
 Psolus patagonicus 0.03/1.22 0.02/2.43 --
 Pseudocnus
 dubiosus leoninus 0.07/2.48 0.16/3.95 0.05/2.03

ECHINOIDEA
 Austrocidaris
 canaliculata 0.32/1.33 -- --
 Sterechinus agassizi 3.36/6.88 2.81/5.43 3.63/8.92

ASTEROIDEA
 Calvptraster sp. 0.85/5.63 0.44/4.46 1.18/5.16
 Cosmasterias lurida 0.33/1.52 -- 0.26/1.75
 Ctenodiscus australis 0.20/2.80 -- 0.31/2.21
 Labidiaster sp. -- -- --

OPHIUROIDEA
 Gorgonocephalus
 chilensis 1.74/2.15 -- --
 Ophiacanta vivopara 7.25/9.92 6.58/10.58 11.65/11.09
 Ophiactis asperula 5.22/7.74 4.45/7.12 11.44/7.19
 Ophiuroglypha lymanii 1.10/4.79 0.10/3.44 0.72/6.15
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Author:Bremec, Claudia; Escolar, Mariana; Schejter, Laura; Genzano, Gabriel
Publication:Journal of Shellfish Research
Article Type:Report
Geographic Code:3ARGE
Date:Apr 1, 2008
Words:6085
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