Using stable isotopes ratios to decipher changes in benthic food webs characteristics along the rapidly warming West Antarctic Peninsula

Against a backdrop of rapid warming along the Western Antarctic Peninsula (WAP), this project aimed to better understand the consequences of the upcoming changes in the biotic and abiotic environments on the the food web of shallow-water benthic communities. In February 2023, the first TANGO expedition, using a sailboat, brought nine scientists from the Belgian Universities of Liège, Ghent and Brussels to WAP. To assess the importance of these changes on the local food web dynamics, five benthic communities were investigated along the WAP, split between two contrasted environments, Dodman Island (Grandidier Channel, 66°S) & Blaiklock Island (Bigourdan Fjord, 67.5°S), with a focus on macroalgae forests (n=2 sites) and sedimentary soft bottoms (n=3 sites). In each station, basal food sources (i.e. POM, SPOM, macroalgae, microphytobenthos) as well as benthic invertebrates (n= 435) were sampled quantitatively to assess their biomass in-situ, and to gather biological material for Stable Isotopes Analysis (SIA). To describe and compare the trophic characteristics from the targeted communities, stable isotope ratios of carbon, nitrogen and sulphur from this material were measured. This allowed to formally represent the different communities in the isotopic space, and to compare their topologies along the environmental gradient studied. This first visualisation revealed important differences in terms of isotopic diversity and topology, both between the two types of habitat sampled and between the two latitudes considered. Altogether, these variations echo the general characteristics of the communities, such as the higher organism biomass measured in the macroalgal forests, which are also more diverse in terms of the number of species sampled. In the near future, these preliminary data will be supplemented by samples collected around the Gerlache Strait (n stations=6, 64.3°S – 65°S) during the TANGO 2024 campaign. By broadening the environmental conditions studied, this should enable us to better understand the evolution of trophic dynamics in these shallow Antarctic benthic ecosystems subject to rapid environmental change.