MEPS 336:151-160 (2007)  -  doi:10.3354/meps336151

Small-scale spatial variability of food partitioning between cultivated oysters and associated suspension-feeding species, as revealed by stable isotopes

Stanislas Dubois1,*, Francis Orvain1, Julio César Marin-Léal1, Michel Ropert2, Sébastien Lefebvre1

1Laboratoire de Biologie et Biotechnologies Marine, Université de Caen, Esplanade de la Paix, 14032 Caen cedex, France
2Laboratoire Environnement Ressource de Normandie, IFREMER, Avenue du Général de Gaulle, BP 32, 14520 Port en Bessin, France

ABSTRACT: Oyster culture structures support a host of epibionts belonging to the same suspension-feeding guild, which are considered to be potential competitors for food with cultivated oysters. In an intertidal shellfish ecosystem on the northern French coast, an approach based on stable isotopes (13C and 15N) was used to investigate intra- and interspecific food resource partitioning among cultivated oysters and the main associated wild sessile epibionts such as polychaetes, barnacles, mussels and ascidians. The main objective of the present study was to determine inter- and intraspecific food partitioning, along with small-scale spatial variability, within the guild of suspension feeders. We demonstrated that interspecific competition was limited among co-occurring suspension-feeders (ascidians, serpulid and terebellid polychaetes, bivalves and barnacles). None of the studied species had similar δ13C and δ15N signatures, indicating that relative contributions of organic matter sources may differ for each suspension-feeding species. Spatial variability was investigated both from the view of intra- and interspecific variability. Intraspecific variability was examined with regard to species’ feeding biology and the trophic plasticity of co-occurring suspension-feeders. Mantel tests indicated that spatial heterogeneity resulted not only from environmental conditions, such as elevation above sea level (a.s.l.) and sediment features, but also from the inherent spatial structure of isotopic signatures. Our results show that isotopic approaches that are limited to sampling in one area and at one time are at risk of mistaking trophic interactions.

KEY WORDS: Shellfish · Oysters · Sessile epibionts · Stable isotopes · Spatial variability · Trophic plasticity

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