Structure, fonctionnement, évolution des communautés benthiques ...

tel-00009359, version 1 - 1 Jun 2005
Chapitre 3 - Fonctionnement du réseau trophique benthique de la Grande Vasière
More widely this study brings to our attention the complex interactions between the target
species and their preys and competitors and suggest that the whole trophic structure could be modified
due to exploitation of the dominant species populations by modifying their size class structure. The
fisheries should take in account the whole network of biotic interactions to increase the efficiency of
management.
This study is a first step in the analysis of the demersal and benthic community of the Great
Mud Bank. It focused on exploited invertebrate and fish species and compared their relative position
in the trophic web with those of their main preys and competitors. Our results indicate that benthic
primary consumers of the Bay of Biscay system are influenced by two food sources reflected in their
δ 13 C signatures. Benthic suspension feeders have a signature relative to POM, while deposit feeders
exhibit a huge enrichment in 13 C. Thus, the diet of benthic suspension feeders is based on a greater
portion of fresh pelagic sedimenting particles as compared to that of deposit feeders, which consume
mainly meio-and microfauna, detritic material and recycled organic matter from the benthic system
with associated bacteria. Large benthic predators such as anglerfish and sharks, which could represent
a fifth trophic level, were not considered in this study. A complex structure was identified within the
trophic web, each of the three main taxonomic groups (crustaceans, polychaetes, fishes) had species in
the different trophic levels which suggests a high specific and functional biodiversity. This implies
that trophic interactions between target and non-target species and their preys must be better
understood in order to optimize exploitation while conserving the biodiversity of this ecosystem. As
the present study was mainly concerned with large epifauna and demersal species, further
investigations need to focus on the sedimentary compartment, including the macrofauna, meiofauna
and bacteria, which are the bases of the benthic food web component.
Acknowledgments. This study was funded by the CNRS, University of Brest and IFREMER. The
authors are grateful to the crews of the RV Côtes de la Manche, Côte d’Aquitaine and Thalassa for
their assistance in collecting samples, and to Charlie Scrimgeour and Norbert Naulet for running
samples, Robert Marc for drawing the map and James Gray and Sorcha Ni Longphuirt for linguistic
assistance. The manuscript was greatly improved by the comments of anonymous referees.
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