Photoadaptation in <i>Phaeocystis pouchetii</i> advected beneath annual sea ice in McMurdo Sound, Antarctica

A bloom of the colonial microalga Phaeocystis pouchetii was advected from ice-free waters to beneath 1.5 m of annual fast ice in East McMurdo Sound, Antarctica in late December 1984. Strategies of photoadaptation to a reduction in growth irradiance involved a 3- to 4-fold increase in photosynthetic efficiency per chlorophyll a (αb) and a 2- to 3-fold increase in photosynthetic efficiency per cell (αc). The index of photoadaptation (Ik) decreased by 50% on both a chlorophyll a and cellular basis. In situ production by Phaeocystis under sea ice in the East Sound is estimated to contribute 16 g carbon m−2 annually, a value comparable with sea ice algal production.