Impact of climate change on the distribution of sponges and cold water corals in the Antarctic and Subantarctic

Climate change and ocean acidification, fuelled by the release of anthropogenic carbon dioxide in the atmosphere, impact the physico-chemical dynamics of the ocean. Current changes are undeniable and their rate is believed to be much faster than anywhere else in the geological records. Modifications of the seawater temperature and pH, amongst other parameters, impact marine organisms across all levels of biological organisation and extinctions or shifts in the distributional range of several species are expected. Unable to escape the alteration of their environment, sedentary benthic organisms are particularly exposed. The fate of corals and sponges, the main habitat-forming species in the benthos, is considered critical because of their aragonite skeleton (corals) and slow growth (sponges). In this thesis, I intended to estimate the impact of climate change and ocean acidification on the distribution of sponges and cold water corals in the Antarctic and the Subantarctic. For this purpose I focused on two main case studies: Case study I: Climate-induced changes in megabenthic communities along the Antarctic Peninsula and their consequences on the distribution of glass sponges. Case study II: Sensitivity of the cold water coral Desmophyllum dianthus to ocean acidification inferred from its distribution along a pH gradient in a Chilean fjord. In both cases, I chose to work mainly with non-destructive sampling devices, namely Remotely Operated Vehicles (ROVs) acquiring underwater videos for quantification of the benthos and simultaneously recording several physico-chemical parameters. For monitoring purposes a standardized method was needed to obtain comparable abundance data from videos recorded by different vehicles.