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

Abstract

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

Particulate Organic Detritus and Detritus Feeders in Coastal Food Webs

“…Other land-derived organic matter, including sewage, terrestrial plant litter, and riverine organic matter, can be much more available (Van Dover et al, 1992;McLeod and Wing, 2009). Peat washed by tidal action becomes assimilated by intertidal suspension feeders, including barnacles and mussels (Sarà et al, 2008). Eroding peat 8000-12 000 years old enters Arctic freshwater (but apparently not marine) food web, resulting in a radiocarbon age of ~1300 years for an oldsquaw duck (Clangula hyemalis) foraging on prey exposed to the ancient peat (Schell, 1983).…”

“…In contrast to oceanic systems fueled primarily by phytoplankton and its relatively short-lived detritus, coastal food webs experience input of fresh and detrital sources of phytoplankton, micro phytobenthos, benthic macroalgae, seagrasses, salt marsh grasses, and mangroves, in addition to a wide range of terres trial organic matter such as leaf litter and soil organic matter. Nevertheless, fossil car bon such as methane (Bauer et al, 1990), peat (Schell, 1983;Sarà et al, 2008), terrestrial organic matter delivered by rivers (McCallister et al, 2004;Caraco et al, 2010) and glaciers (Hood et al, 2009), and even 365-million-year-old shale (Petsch et al, 2001) can become available for biological uptake. Many of these food sources enter the food web primarily as detritus, though the importance of specialized grazers is worthy of attention.…”