BiodiveRsity Under rapid environmenTAL change: trophic interactions and communities’ responses in austral benthic ecosystems.

The coastal benthic ecosystems of the Southern Ocean are strongly structured by sea ice dynamics, light availability, and glacial disturbances. Rapid environmental changes observed along the western Antarctic Peninsula are causing changes in the nature, seasonality, and flows of organic matter to the benthos. This thesis aims to analyze the influence of food source diversity and availability on the trophic regimes of Antarctic benthic consumers. An approach combining fatty acid and highly branched isoprenoid (HBI) analysis was used to characterize the origin of assimilated organic matter and to discriminate the relative influence of sympagic production. Samples were collected from various habitats along the western Antarctic Peninsula and the Magellan Strait. The analyses focused on primary food sources and benthic consumers belonging to several trophic guilds. The results reveal different feeding strategies depending on the species and habitat. Grazers have contrasting diets, reflecting varying capacities to exploit benthic resources, while suspension and deposit feeders closely reflect particle dynamics. The results as a whole highlight the key role of local environmental conditions in the structure of benthic food webs and highlight the implications of climate change for the functioning of Antarctic coastal ecosystems.