Vitamin B₁₂ in Marine Ecology

Abstract

AT least half the marine algal flagellates and diatoms which have been studied in pure culture have been shown¹ to require an exogenous source of vitamin B₁₂, which is the reason for an interest in the occurrence of this vitamin in the sea as one of the factors controlling phytoplankton populations and the productivity of water masses. However, the amount of vitamin required is very small ; just how small is not generally realized, and it may be that the amount found in the sea is never sufficiently low for an ecological control to be exerted on any of the comparatively very sparse populations of phytoplankton which happen to require the vitamin. Whether, in fact, this is so cannot be decided directly with natural populations for a number of reasons, but it has been possible to determine the magnitude of the requirement of vitamin B₁₂ in one marine organism and then, assuming algae requiring vitamin B₁₂ to be alike in this respect, to apply the result to data on marine populations and to assays of sea water for vitamin B₁₂.