Modeling the distribution of Cold Water Corals in the Weddell Sea-Antarctica (present and future).

Supervisor: Kerstin Jerosh (Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research).
Interests in exploring Cold Water Corals (CWC) ecosystems witnessed a dramatic increase in the last decades, after the realisation that their habitats are threatened by ocean warming and acidification. However, they are still largely overlooked by the scientific community in deep and harsh environments like the Southern Ocean. Recent advances in species distribution models (SDM) have allowed forecasting species distribution patterns and assessing climate change impacts at different spatial scales. Several limitations related to the accuracy of species presences, the lack of reliable absence data and the limited spatial resolution of environmental factors, have restricted the widespread utilisation of these approaches in polar areas. In this work, nine species distribution modelling algorithms were merged within the ensemble forecasting platform ‘biomod2’ to generate the global habitat suitability for Scleractinian corals, in the Weddell Sea. For this purpose, real presence-absence records of 13 species were gathered from research expeditions and literature and a final set of 14 high-resolution environmental variables was pre-selected. Response of Scleractinians’ distribution to the future climate change was also investigated, based on five future scenarios of the bottom sea temperature. Present ensemble prediction maps accurately captured the potential ecological niches of the modelled species (good to excellent true skill statistic (TSS) and area under the receiver operating characteristic curve (AUC) evaluation measures). In the Weddell Sea, Scleractinian distribution is limited to the continental shelf and slope areas with preference to small scale features (i.e., seamounts), which have been identified as having a high probability of supporting cold-water coral habitat. The most important factors in determining CWC habitat suitability were distance to coast and ice shelves, bathymetry, calcium carbonate and temperature. The response of Scleractinian to future climate revealed some changes in small-scale spatial distribution patterns. Under warmer conditions, the CWC is expected to expand their distribution range by a total of 6 to 10% compared to the present. This expansion will concern the Filchner Trough and the adjacent continental shelves as well as the eastern side of the Antarctic Penisnula. In contrast, under colder conditions, the probability of occurrence of CWC is expected to decrease by 44% mainly off the continental shelf of Coats Land and Queen Maud Land, by 2099.

Keywords: CWC, SDM, biomod2, Scleractinian, Weddell Sea, climate change