Latitudinal and temporal variability in the community structure and fatty acid composition of deep-sea nematodes in the Southern Ocean

This study describes and combines structural and functional aspects of deep-sea nematode assemblages from the Atlantic sector of the Southern Ocean. Samples were collected at six stations along the Prime Meridian (49–70°S), including a repeated sampling after one and a half months interval at the Polar Front (52°S), where meanwhile a seasonal phytoplankton bloom had settled. The aim was to gain insight in the latitudinal and temporal variability in nematode community structure and diet based on the generic composition and bulk fatty acid composition of the community, respectively. The results show that nematode assemblages along the transect differed relatively little and that they were all highly comparable to slope and abyssal communities elsewhere in the world in terms of nematode standing stock, diversity and composition. Nematode community composition was only weakly correlated with the community fatty acid composition, indicating that simply the occurrence of distinct genera or the proportion of nematode feeding types based on mouth morphology, cannot explain the variance in FA compositions of the communities. Moreover, the generally low FA content of nematodes suggests that they do not accumulate lipids for energy storage and that they may feed throughout the year on constantly available food sources. A year-round foraging activity could also explain the recorded lack of food uptake as a short-term response to the recently settled phytodetritus at the revisited Polar Front station. Nevertheless, the higher relative abundance of nematodes in the top centimeter layer of the sediment and the occurrence of the genus Leptolaimus only after phytodetritus had settled at the seafloor, suggests the recording of an early stage in a delayed response to the seasonal event.