PRIMARY PRODUCTIVITY AND CALCIFICATION RATE IN BLOOMS OF THE COCCOLITHOPHORID EMILIANIA-HUXLEYI (LOHMANN) HAY-ET-MOHLER DEVELOPING IN MESOCOSMS

Primary production and calcification rate were monitored in mesocosms with different nutrient conditions at the Marine Biological Field Stat ion 20 km south of Bergen, Norway. The incorporation of carbon in part iculate organic matter (POC) and of calcium in calcite was measured wi th the radioactive isotopes C-14 and Ca-45, respectively. It appeared that under eutrophic conditions daily POC production in the algal size fraction > 10 mum eventually reached a higher level than in the < 10 mum algae, which was probably the result of size-selective grazing of the smaller algae by microzooplankton. At oligotrophic conditions the < 10 mum algae became the dominant producers. In two of the mesocosms studied blooms of the coccolithophorid Emiliania huxleyi (Lohmann) Hay et Mohler developed. Indirect evidence shows that after culmination o f the blooms both the POC content in the size fraction < 10 mum (to wh ich E. huxleyi belongs) and the calcite content were strongly reduced. Bloom decline probably resulted from the massive lysis of E. huxleyi cells leading to the remineralization of POC and the dissolution of ca lcite. No trend in the coccolith formation rate per cell could be disc overed during the growing phase of the blooms. Evidence is also presen ted that the light saturation level for calcification was low and that this process may have taken place even in the absence of light.