Trophic ecology of the rocky shore community associated with the Ascophyllum nodosum zone (Roscoff, France): A delta C-13 vs delta N-15 investigation

This study aimed to characterize the structure and functioning of the benthic food web associated with the Ascophyllum nodosum zone of the rocky shore of Roscoff by using delta C-13 and delta N-15. Several characteristics of the trophic ecology of the invertebrates associated with this mid-littoral habitat and which belong to different functional groups (e.g., grazers, filter-feeders, predators and omnivores) were highlighted. In particular, the filter feeder species (including mostly sponges) used macroalgae-derived organic matter as a substantial food requirement. The results also pointed out an important stable isotopes variability for strict coexisting primary consumers which: (1) is directly related to the high delta N-15 range of the food sources; (2) makes it impossible to establish a unique trophic level scale based on delta N-15 values, as previously done in coastal environments; and (3) points out the existence of major co-occurring trophic pathways which characterise the Ascophyllum nodosum habitat. (C) 2008 Elsevier Ltd. All rights reserved.