CALCIFYING PHYTOPLANKTON IN BJORNAFJORDEN, NORWAY - THE PREBLOOM SITUATION

Various physical, chemical and biological parameters were followed ove r a two week period prior to the blooming of the coccolithophorid Emil iania huxleyi (Lohmann) Hay et Mohler in Bjornafjorden (western Norway ). Total inorganic carbon concentrations and pCO2 profiles showed low values at the surface, due to freshwater influence. Such low values ma y be of competitive advantage for phytoplankton like coccolithophorids capable of utilising bicarbonate besides CO2 as an inorganic carbon s ource for growth. Low nutrient concentrations in the surface limited d ense bloom formation here. Subsurface bloom formation was restricted b ecause of the poor incident irradiance conditions. The assimilation nu mber was low (varying between 3.16 and 15.88 mg C mg chl a-1 day-1, me an 7.82 mg C mg chl a-1 day-1). Calcification rate of E. huxleyi incre ased gradually over the sampling period, but did not exceed 11% of tot al inorganic carbon assimilation by the end of the survey. In general the phytoplankton population consisted of various spring diatoms, dino flagellates and Euglenophyceae; E. huxleyi was not abundant, but incre ased in numbers (surface values) from 32000 to close to 175000 cells p er litre by the end of the period, which can be regarded as a non-bloo m condition. The turnover of the phytoplankton biomass was high; 66.1% (s.d. 38.1, n = 7) of the phytoplankton primary production was grazed on a daily basis; predominantly by copepods. In addition 21.8% (s.d. 40.8%) of primary production resulted in an actual increase in phytopl ankton standing stock.