The role of benthic amphipods in the eastern Weddell Sea trophic web as determined from stable isotope and fatty acid analyses

Within the Southern Ocean, amphipods have achieved a conspicuous adaptative radiation which gave rise to the development of numerous feeding strategies (Jazdzewski et al. 1996; Dauby et al. in press; De Broyer et al. in press). The discrepancy between the ecological significance of amphipods in the Antarctic and our poor knowledge of their ecofunctional role calls for a more detailed investigation of their importance in this ecosystem trophodynamics.
This study focused on the eight amphipods species which were collected and from which isotopic and lipidic (when available) (Graeve et al. in press) compositions were compared to their respective gut contents previously described (Dauby et al. in press). The interest of both first techniques rely upon the direct relationship between the isotopic signatures and the lipid composition of organisms and those of their diet (De Niro and Epstein 1978, 1981; Peterson and Fry 1987; Graeve et al. 1994; Cripps et al 1999).
Amphipod stable isotope ratios and fatty acids composition correspond rather accurately to the trophic classification based on gut contents and attest to their high spectrum of feeding types. Since the fundamental difference between the approaches to diet studies is the time scale each method addresses, this coincidence indicates that there would be no significant changes in feeding strategies over time. Three levels of the food web are covered by the eight species and, instead of belonging strictly to one trophic category, amphipods display a continuum of values from the suspension-feeder to scavengers.