Abstract
Primary production and calcification rate were monitored in mesocosms with different nutrient conditions at the Marine Biological Field Station 20 km south of Bergen, Norway. The incorporation of carbon in particulate orfianic matter (POC) and of calcium in calcite was measured with the radioactive isotopes 14C and 45Ca, respectively. It appeared that under eutrophic conditions daily poe production in the algal size fraction < 10 µm eventually reached a higher level than in the < 10 µm algae, which was probably the result of size-selective grazing of the smaller algae by microzooplankton. At oligotrophic conditions the < 10 µm 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 of the blooms both the poe content in the size fraction < 10 µm (to which 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 poe and the dissolution of calcite. No trend in the coccolith formation rate per cell could be discovered during the growing phase of the blooms. Evidence is also presented that the light saturation level for calcification was low and that this process may have taken place even in the absence of light.
