From the pelagic subantarctic ecoregionalisation to Marine Protected Areas in the high seas

The North Indian sector of the Southern Ocean and the South Indian Ocean are geographical zones with strongly contrasting physical and chemical characteristics within a small latitudinal range. This strong oceanographic contrast, coupled with the action of the Antarctic Circumpolar Current, causes the formation of oceanographic fronts that separate the different water masses according to their environmental characteristics. These regional characteristics have a major influence on the biodiversity of the sub-Antarctic islands, in particular on the spatial distribution of zooplankton and nekton species, which are important food resources for top predators living on the islands in the sub-Antarctic zone. However, global change is likely to have a major impact on the biogeography of these organisms, which are essential for the functioning of sub-Antarctic marine ecosystems, in particular by causing a southward shift in the range of these species.

The aim of this thesis is to propose a pelagic ecoregionalisation of the Indian Ocean sector and to study the consequences of future climate change on these ecoregions in order to propose future deep-sea marine protected areas in the sub-Antarctic region. To this end, four objectives were defined:

1. To complete the descriptive atlases of the abiotic and biotic conditions of the sub-Antarctic marine ecosystem in order to identify the species and communities of importance for the Indian sub-Antarctic.
2. To model the spatial distribution of key species and communities in the sub-Antarctic marine ecosystem in order to identify pelagic ecoregions.
3. Assess the impact of global change on the future distribution of the identified pelagic ecoregions.
4. Identify priority areas for conservation with a view to establishing MPAs on the high seas in the CCAMLR area to complement existing MPAs in the sub-Antarctic EEZ.