Bentho-pelagic coupling at Potter Cove, Antarctica: A fatty acid approach.

MARTIN GRAEVE; RICARDO SAHADE; VERÓNICA FUENTES; MARCOS TATIÁN; GERHARD KATTNER

POLARFORSCHUNG

Año: 2008 vol. 571 p. 147 - 153

0032-2490

Antarctic benthic communities are diverse and rich in biomass. A striking feature is the dominance of benthic filter feeders in most of the studied areas (Arntz et al. 1994, Barnes 2005, Gili et al. 2006). The biology of these filter feeders is usually linked to the strong seasonality of the primary production, characteristic for polar ecosystems (Clarke 1996). However, this linkage could be much more important in shallow coastal ecosystems than in deeper continental shelf areas, because a clear and direct coupling between primary pelagic and secondary benthic production is an obvious feature in shallow waters (Dayton and Oliver 1977, Clarke 1996, Cattaneo-Vietti et al. 1999, Corbisier et al. 2004). At Potter Cove planktonic primary production is low, and the phytoplankton blooms, which are characteristic for other Antarctic coastal areas, are almost absent (Schloss and Ferreyra 2002), while the benthic secondary production is characterised by high densities and biomass of benthic suspension feeders, especially bivalves, pennatulids, ascidians and sponges (Sahade et al. 1998, Sahade et al. this issue). Moreover, it was an unusual finding that two of the most successful ascidians Molgula pedunculata and Cnemidocarpa verrucosa do have their reproductive season during winter, totally uncoupled from summer primary production pulses (Sahade et al. 2004). This suggest that either ascidians are able to store energy for reproduction, or the energy demand of the benthic  filter feeders during winter is not as high as usually assumed (Gili et al. 1996, Ahn et al. 2003). Therefore, the main energy source for this benthic community is probably not based on local primary production. Reinforcing this idea, particles analysed in ascidian gut during a year-round period revealed only little micro-algae contribution, even during summer (Tatián et al. 2004). To study food web interactions and possible energy sources, fatty acid trophic markers are a useful tool. This is due to the fact that specific fatty acids are transferred almost unchanged from algae into the lipids of higher trophic organisms and top predators (Dalsgaard et al. 2003). For instance, typical fatty acid markers of diatoms are 16:1(n-7) and 20:5(n-3) and of dinoflagellates 18:4(n-3) and 22:6(n-3). In addition, long-chain fatty acids like 20:1(n-9) and 22:1(n-11) are major fatty acids of calanoid copepods, which could play an important role providing energy to the benthic system (Graeve et al. 1997, Lee et al. 2006). These fatty acids, which may be part of their ingested material, can be egested with faecal pellets, which have high sedimentation rates, thus contributing to the carbon flux to the benthic system. In this study, fatty acid compositions of particulate material of water column and sediments, and benthic suspension-feeders are used to trace the possible origin and pathway of the energy flux that fuels the benthic ecosystem in Antarctic shallow waters.