Carbon sources of Antarctic nematodes as revealed by natural carbon isotope ratios and a pulse-chase experiment

delta C-13 of nematode communities in 27 sites was analyzed, spanning a large depth range (from 130 to 2,021 m) in five Antarctic regions, and compared to isotopic signatures of sediment organic matter. Sediment organic matter delta C-13 ranged from -24.4 to -21.9 parts per thousand without significant differences between regions, substrate types or depths. Nematode delta C-13 showed a larger range, from -34.6 to -19.3 parts per thousand, and was more depleted than sediment organic matter typically by 1 parts per thousand and by up to 3 parts per thousand in silty substrata. These, and the isotopically heavy meiofauna at some stations, suggest substantial selectivity of some meiofauna for specific components of the sedimenting plankton. However, delta C-13-depletion in lipids and a potential contribution of chemoautotrophic carbon in the diet of the abundant genus Sabatieria may confound this interpretation. Carbon sources for Antarctic nematodes were also explored by means of an experiment in which the fate of a fresh pulse of labile carbon to the benthos was followed. This organic carbon was remineralized at a rate (11-20 mg C m(-2) day(-1)) comparable to mineralization rates in continental slope sediments. There was no lag between sedimentation and mineralization; uptake by nematodes, however, did show such a lag. Nematodes contributed negligibly to benthic carbon mineralization.