Suspension feeders as natural sentinels of the spatial variability in food sources in an Antarctic fjord: A stable isotope approach

We examined the effect of glacial melt-related retreat environmental conditions on the spatial heterogeneity of food sources for Antarctic nearshore marine benthic communities of Potter Cove, a representative fjord on King George Island on the West Antarctic Peninsula. Focusing on Antarctic suspension feeders, we surveyed the variation of carbon (delta C-13) and nitrogen (delta N-15) stable isotopes in three different stations with contrasting characteristics in terms of glacier-sedimentary regimes and distance from the glacier. Bayesian mixing models were used to estimate the relative contribution of eight potential food sources at the study sites and to the consumers' diet. The isotopically signatures of suspension feeders displayed a broad range of assimilate available food sources with distinct contributions at each site. Overall, for most of the suspension feeders analysed, contributions of suspended particulate matter and macroalgae detritus tended to prevail over the rest of the potential food sources. Additionally, we confirm the assimilation of krill faeces by benthic organisms reinforcing its relevance as food source in nearshore Antarctic ecosystems. Mixing models corroborated the influence of glacier discharge on the spatial distribution of available food sources, since their contribution in the suspension feeders diet was different and more heterogeneous in the internal stations (ice-proximal zone) than in the external one (ice-distal zone). The analysis of isotopic signatures of primary benthic consumers (suspension feeders) indicated the spatial heterogeneity of food sources and its composition in coastal Antarctic nearshore, as consequence of the glacial influence on the local environment and hydrology.