In the Southern Ocean, during the ANT-XXVIII expedition (RV Polarstern), four stations contrasting in terms of surface primary productivity were studied along the Polar Front from 39°W to 10°E. We investigated to what extent differences in surface primary productivity, together with benthic environmental parameters (concentration of Chlorophyll a and its derivatives, and sediment fatty acid composition) mirrored in nematode standing stocks (i.e. density and biomass) and differences in community composition. Moreover, nematode fatty acid (FA) analyses were performed to unravel feeding selectivity patterns on “bulk” nematodes and particular nematode taxa (Desmodora and Desmoscolecidae). South Georgia station, located NW of South Georgia island, possessed not only highest surface primary productivity, but also highest Chlorophyll a (and its derivatives) and total sediment FA concentrations, also reflected in up to 10-fold higher nematode standing stocks. FA composition from “bulk” nematodes, Desmodora and desmoscolecids revealed a planktonic-based diet, as revealed by diatom biomarkers ((16:1w7)/(16:0) > 1)for “bulk” nematodes and Desmodora from South Georgia. Nematodes at the other stations situated more to the east showed non-selectivity for fresh diatom material based on the FA composition, associated with low surface primary productivity and low labile carbon concentrations (low Chlorophyll a values) in these areas. Uncommonly found in typical deep-sea environments, the nematode genus Desmodora exhibited high numbers at South Georgia station, probably as a response to the high primary productivity at the surface, confirming the strong benthic–pelagic coupling even at great depths. This study suggests that alterations in nematode standing stocks and community composition, together with selective feeding reflected by distinct FA composition, can be positively associated and shaped by surface productivity regimes. |
