Seasonal vitamin B12 and phytoplankton distribution near Napeague Bay, New York (Block Island Sound)1

Abstract

Vitamin B12 levels in seawater were assayed over a 13‐month period with Thalassiosira pseudonana Hasle et Heimdal, clone 3H. Concentrations at four different stations ranged from undetectable to 10.6 ng·liter−1. Concentrations during November– December 1975 were undetectable and may have limited the growth of B12 auxotrophic phytoplankters. A positive significant correlation, on a seasonal cycle, was found between B12 levels and dinoflagellate cell numbers and negative significant correlations between B12 and chlorophyll a concentrations at the same two stations. B12 levels were highest during summer when other nutrients (NO3−‐N, PO43−‐P) were low. Bacterial production is suggested as a source of the summer concentrations.