Geographic range shift responses to climate change by Antarctic benthos: where we should look

Toleration, adaptation, migration or extinction are the options for species making up Southern Ocean (SO) shelf biodiversity, in response to accelerating change (e.g. warming), Physiological evidence suggests few organisms may tolerate, and slow generational turn-over means fewer will adapt to, unprecedented change. To avoid extinction many organisms must migrate along linear coast, go deeper or both. There is strong evidence that such range shifts are happening, and occurred in the past, along N-S (linear) coastlines (e.g. USA), but there are no continuous shelf/slope connections to Antarctica from elsewhere. There are only 3 major linear shelves in Antarctica: Victoria Land, the Antarctic Peninsula, and the Kerguelen Plateau. Scientific effort has focused on the former two but their temperature gradient is negligible or bi-directional, so most potential for thermally-driven range shifts lies along the Kerguelen Plateau. We investigated ranges of several SO taxa (bivalve and gastropod molluscs, amphipods, ophiuroids and hexacorals), and looked for hotspots of where the geographical range limits of different species coincided. Southern Patagonia, South Georgia and Kerguelen had amongst the greatest range-limit hotspots. Shifts of SO endemics will be mainly range contractions (of northernmost limits), whilst species with ranges crossing the Polar Front (PF; the strongest jet of the Antarctic Circumpolar Current) may become 'new' SO endemics. Species with southernmost limits north of the PF should penetrate the SO, either as returning natives (expelled during glaciations) or invasive non-indigenous species. Monitoring range shifts in only a few suggested key places and taxa should give powerful insights into biodiversity responses and gauge tolerance vs. migration.