Role of peat organic matter on isotopic composition of most abundant benthic organisms in intertidal habitats of SW Iceland

The transfer of peat organic matter (OM) fromtidal pools of upper littoral to downstream rocky shores andits potential incorporation into marine biota were investigatedusing the stable isotope approach. Samplings werecarried out in September 2004 in two SW Icelandic sites(Osar and Hvassahraun), where we selected (1) areas withshores where grass gently declined towards rocks and, onreaching the sea line, formed small tidal peat pools and (2)areas where grass and rocky shores were not contiguous,rather the grass lower limits were several hundreds ofmeters back from the shore. In both grass and no grassareas, in the intertidal zone, all benthic organisms and allpotential OM sources were sampled. Dominant macroalgaewere Ascophyllum nodosum ([Linnaeus] Le Jolis) andFucus vesiculosus Linnaeus. In grass sites, organisms partially reXected the isotopic composition of peat OM,while in no grass sites, peat represented only a negligibleamount of available OM, or its signal was totally absentfrom the environment. Intertidal organisms could rely onpeat both directly by suspension feeding, grazing or scavengingand indirectly by predation (crabs) on low level consumers(barnacles).