Ecophysiological plasticity in the Arctic phytoplankton species Phaeocystis pouchetii (Prymnesiophyceae, Haptophyta)

The colony forming phytoplankton species Phaeocystis pouchetii plays a key role in nutrient turnover and the fixation of inorganic carbon in the Arctic and sub-Arctic Ocean. In the Fram Strait, salinity is a variable parameter due to freezing and melting processes of sea ice and due to a bidirectional current regime providing the exchange of water masses between the Arctic and Atlantic Ocean. We tested the growth response of seven P. pouchetii strains to six different salinities (7–60) in order to identify ecotypes adapted to specific environmental regimes. The experimental setup was realized by means of a custom-build incubator enabling ecophysiological treatments at low temperatures combined with high irradiances. Salinity tolerance showed a heterogenic, strain specific pattern varying from broad (salinity 60) to relatively narrow ranges (salinity 33–45) indicating an ecophysiological differentiation which is rather dependent on the sampling period than on the geographical origin. In order to confirm these findings it is however necessary to obtain data from strains isolated in the same year or even from the same bloom. The ecotype question can only be solved when methodical constraints concerning molecular taxonomy of P. pouchetii are resolved.