Understanding the factors that determine the distribution of taxa at various spatial scales is a crucial challenge in the context of global climate change. This holds particularly true for polar marine biota that are composed of both highly adapted and vulnerable faunas. We analysed the distribution of 2 Antarctic echinoid species, Sterechinus antarcticus and S. neumayeri, at the scale of the entire Southern Ocean using 2 niche modelling procedures. The performance of distribution models was tested with regard to the known ecology of the species. The respective contributions of environmental parameters are discussed along with the putative roles played by biotic interactions and biogeographic processes. Depth was the parameter that contributed most to both distribution models, whereas sea ice coverage and sea surface temperature had significant contributions for S. neumayeri only. Suitability maps of the 2 species were mostly similar, with a few notable differences. The Campbell Plateau and Tasmania were predicted as suitable areas for S. antarcticus only, while S. neumayeri was restricted to the south of the Antarctic Polar Front. However, numerous sampling data attest that S. antarcticus is absent from the Campbell Plateau and from Tasmania. Different hypotheses are formulated to explain the mismatch between observed and modelled distribution data. They stress the putative roles played by both oceanographic barriers to dispersal (Antarctic Polar Front), biotic factors (species exclusion patterns) and biogeographic processes (ongoing dispersal).
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