Adaptation to fluctuating light and iron limitation by Phaeocystis antarctica

Abstract

The marine phytoplankton genus Phaeocystis has a world-wide distribution and is able to form almost uni-algal blooms in coastal areas and in polar regions. Notwithstanding its successfulness in plankton communities, only little is know about its physiological ability to adapt to multiple stress regimes as prevailing in the Southern Ocean: fluctuating light as a result of strong vertical mixing and iron limitation. Under such conditions, cells are jeopardised by photoinhibition. Previous experiments under iron-limitation have shown that, besides a shift in the ratio of diatoxanthin to diadinoxanthin, Phaeocystis exhibits shifts in the pool of butanoyloxyfucoxanthin, hexanoyloxyfucoxanthin and fucoxanthin. It was hypothesised that a possible fucoxanthin cycle is an additional means of dissipating excess light energy under iron limitation. Here we present data on photoacclimation, as measured by fluorescence parameters, in vivo absorption and pigmentation, in lab experiments with Phaeocystis antarctica. Experiments were performed with iron-deplete and iron-replete cultures under conditions of fluctuating light, mimicking vertical mixing.