Trophic ecology of nematodes from various microhabitats of the Roscoff Aber Bay (France): importance of stranded macroalgae evidenced through delta C-13 and delta N-15

Spatial and temporal diversity of food sources of intertidal nematodes of 3 different feeding habitats (estuarine muddy sediments, Spartina maritima and Juncus maritimus marshes) in the Roscoff Aber Bay, France, was assessed by the use of delta(13)C and delta(15)N values. Within the bay, nematodes largely dominated within the total meiofauna. Throughout the 3 sampling periods, the delta(13)C and delta(15)N values for nematodes and sources showed that the dominant sedimentary organic matter sources within the 3 microhabitats considered, namely terrigeneous inputs, detrital Spartina maritima or Juncus maritimus and marine POM, did not contribute a significant part of the diet to locally occurring nematodes. In fact, the delta(13)C and delta(15)N values indicate that organic matter derived from stranded macroalgae, mostly Enteromorpha sp. and Fucus spiralis, was the primary contributor to the assimilated food sources of nematodes; more readily utilisable sources (i.e. benthic diatoms) are virtually absent. The present work provides evidence that detrital pathways, including stranded macroalgae from nearby rocks and free-living nematodes, play a key role in the trophic ecology of intertidal flat areas.