Effects of cobalt and vitamin B 12 on the growth of Chrysochromulina polylepis (Prymnesiophyceae)

Atlantic sea water with a low cobalt (Co) concentration (0.02 nM) was enriched with Co additions (0.2, 0.5, 1.0 and 3.0 nM), inoculated with a monoculture of Chrysochromulina polylepis Manton & Parke and incubated under laboratory conditions. Co additions (as a Salt) increased the yield (number of cells) of C. Polylepis. Biomass production was not markedly different if a chelator (EDTA) was added together with Co or if Co was added as vitamin B12 (cyanocobalamin). The maximal growth rate of C. polylepis was 0.8 d−1. Growth rate during the exponential phase was not influenced by Co concentrations, possibly due to Co Contamination. The cell quota of Co for C. polylepis in the stationary growth phase was estimated at 0.55 to 0.69 fg Co cell−1 based on cell yield in relation to Co uptake and 0.55 to 0.70 fg Co cell−1 based on analysis of cells. In the 1988 C. polylepis bloom in the Kattegat and Skagerrak, cell concentrations reached levels of 100 x 106 cells l−1, requiring a Co supply of at least 1 nM. Concentrations of Co in the Kattegat are below 0.5 nM, implying possible Co control of C. polylepis biomass accumulation.