Macrozooplankton from Crozet to Kerguelen and subtropical southern Indian Ocean

The recent Biogeographic Atlas of the Southern Ocean (De Broyer et al., 2014) synthesises knowledge of this ocean's biodiversity from historical explorations to now. It includes a tremendous amount of data from the International Polar Year (2007-2009) and the Census of Antarctic Marine Life - CAML (2005-2010). CAML did not focus on the subantarctic zone. The results of the Atlas for euphausiids (Cuzin et al., 2014) and fish (Duhamel et al., 2014) showed that the area around the Kerguelen Islands was well sampled, but not the rest of the Indian Ocean and even less so the Crozet Islands. The biogeographic atlas confirmed the latitudinal zonation of Southern Ocean fauna according to the major northern fronts (Antarctic, subantarctic and subtropical). However, in the oceanic areas of the Crozet and Kerguelen Islands, this pattern is unusual, due to the geographical narrowing of some of these fronts in relation to the archipelagos in question. This oceanographic situation is therefore of great interest in terms of understanding the biogeographical role of each of the fronts. For example, when studying the spatial distribution of fish larvae (many of which are mesopelagic), Koubbi (1993) showed that the Subantarctic Front is a major biogeographic barrier in this sector. This has been confirmed by the biogeographic analysis of the Myctophidae carried out by Koubbi et al. (2011). The present study therefore aims to test the importance of different hydrological zones on the spatial distribution of macrozooplankton, some of which are prey for marine birds and mammals (e.g. euphausiids and amphipods). Other organisms, such as salps or siphonophores, can also be considered as indicators of the water masses.