Dominant amphipods ofPosidonia oceanicaseagrass meadows display considerable trophic diversity

• DOI: 10.1111/maec.12194
• Publication Date: 2014-10-03T09:29:58Z
• Authors: Loïc N. Michel; Patrick Dauby; Sylvie Gobert; Martin Graeve; Fabienne Nyssen; Nicolas Thelen; Gilles Lepoint
• Keywords: 0106 biological sciences; 14. Life underwater; 15. Life on land; 01 natural sciences

AbstractGut content examination and trophic markers (fatty acids, stable isotopes of C and N) were combined to delineate the diet of the dominant species of amphipods from MediterraneanPosidonia oceanicaseagrass meadows and to highlight trophic diversity among this community. Our results indicate that, although all dominant species heavily relied on macroalgal epiphytes, considerable interspecific dietary differences existed. Carbon stable isotope ratios notably showed that some of the amphipod species favored grazing on epiphytes from leaves or litter fragments (Apherusa chiereghinii,Aora spinicornis,Gammarus aequicauda), while others such asDexamine spiniventrispreferred epiphytes from rhizomes. The remaining amphipods (Caprella acanthifera, Ampithoe helleriandGammarella fucicola) readily consumed both groups. In addition, SIAR modeling suggested that most species had a mixed diet, and relied on several food items. Fatty acid analysis and gut contents revealed that contributions of microepiphytic diatoms and of benthic and suspended particulate organic matter to the diet of amphipods were anecdotal. None of the examined species seemed to graze on their seagrass host [low 18:2(n‐6) and 18:3(n‐3) fatty acids contents], butGammarus aequicaudapartly relied on seagrass leaf detritus, as demonstrated by the lesser13C‐depletion of their tissues. Overall, our findings suggest that amphipods, because of their importance in the transfer of organic matter from primary producers and detritus to higher rank consumers, are key items inP. oceanica‐associated food webs.