Southern Ocean Emiliania huxleyi coccolithophorid populations exhibit different ecophysiology and vulnerability to ocean acidification compared to Northern Hemisphere counterparts

Chair: Jean-Pierre Gattuso

Gustaaf Hallegraeff(1), Joana Cubillos(1), Suellen Cook(1), Lisa Harding(1), Daniel Helm(1), Isobel Thomas(1), Karen Westwood(2), Simon Wright(2), Marius Müller(3)

(1)Institute for Marine and Antarctic Studies, University of Tasmania, Private Bag 129, Hobart, Tasmania 7001, Australia;(2) Australian Antarctic Division, Channel Highway, Kingston, Tasmania 7050, Australia;(3) Instituto Oceanográfico da Universidade de São Paulo, Praça do Oceanográfico 191, São Paulo, SP 05508-120, Brazil.

Southern Ocean Emiliania huxleyi coccolithophorid populations comprise three distinct morphotypes: A, A overcalcified and the weakly calcified B/C. Morphotype A ‘overcalcified’ mainly occurs north of the Subantarctic Front and is replaced by the weakly calcified B/C between the Subantarctic Front and Southern Antarctic Circumpolar Current Front. Morphotype B/C (designated var aurorae) is a Southern Ocean specialist, and genetically and physiologically distinct from well-studied Northern Hemisphere populations (dominated by morphotype A). Under future ocean acidification experimental scenarios, all ecotypes reduced their rate of calcification but with the cold-water adapted ecotype B/C the most sensitive, and ceasing calcification at pCO2 levels above 1000 μatm. Future surveys for E. huxleyi cells in the Southern Ocean therefore should include the capability of recognising “naked cells” by molecular tools. We argue that the distinct differences in the physiological response of the three dominate Southern Ocean ecotypes will have implications for future coccolithophorid community structures and thereby the Southern Ocean carbon cycle.