PRIMARY PRODUCTION, CALCIFICATION AND MACROMOLECULAR-SYNTHESIS IN A BLOOM OF THE COCCOLITHOPHORE EMILIANIA-HUXLEYI IN THE NORTH-SEA

Photosynthesis, calcification and the patterns of carbon (C) incorpora tion into different biomolecules were investigated during a bloom of t he coccolithophore Emiliania huxleyi in the North Sea during June and July 1994. The bloom was confined to an area of ca 3000 km(2) centred at 59 degrees 50'N, 00 degrees 42'E and characterized by enhanced ther mal stability and low nitrate concentrations in the upper mixed layer. Surface E. huxleyi densities within the bloom area ranged between 1 a nd 6 x 10(6) cells l(-1). The mesoscale distribution of E. huxleyi abu ndance suggested that the bloom formation was related to the presence of low concentrations of nitrate rather than phosphate. The bloom was sampled during an early stage of its development, as indicated by the low calcite-C levels (<50 mg C m(-3)), the low calcite-C to particulat e organic carbon (POC) ratio (<0.25) and the low density of detached c occoliths (2 to 3 x 10(4) ml(-1)). Reduced levels of chlorophyll a (<4 5 mg m(-2)) and productivity (<1.2 g C m(-2) d(-1)) were measured in t he coccolithophore-rich waters as compared to stations outside the blo om area. Typical calcification rates within the bloom were 135 mg C m( -2) d(-1), representing up to 20% of the total C incorporation. Relati ve C incorporation into lipids in coccolithophore-rich waters was 1.5 times higher than outside the bloom area. Most of the recently synthes ized lipid (70 to 90%) belonged to the neutral lipid fraction. The enh anced Lipid synthesis resulted in a higher Lipid content of the partic ulate matter. The relationships between irradiance and photosynthate p artitioning consistently showed that C is preferentially channeled int o the protein fraction at low light levels, whereas the relative synth esis of lipids increases only at high irradiances. These metabolic res ponses are discussed in relation to the development of E. huxleyi-rich assemblages. It is concluded that the observed patterns of C incorpor ation represent a general strategy of energy utilization that is also attributable to other groups of marine phytoplankton.