Some ecologically important phytoplankters released vitamins into culture medium during growth. Skeletonema costatum and Stephanopyxis turris (vitamin B12-requirers) produced both thiamine (vitamin B1) and biotin when growing with either 12 or 2 ng vitamin B12/liter. Gonyaulax polyedra (vitamin B12-requirer) produced thiamine with 12 ng vitamin B12/liter, and Coccolithus huxleyi (thiamine-requirer) produced vitamin B12 and biotin with 120 ng thiamine/liter, but only biotin with 10 ng thiamine/liter. The amount of vitamin produced by an alga and rate at which it was produced varied with the phytoplankter, the concentration of the required vitamin, and incubation time. Vitamins produced during early and exponential growth were due to excretions, and those produced at stationary growth resulted from excretion and release due to cell lysis.
Uptake of the required vitamin by all phytoplankters was greatest during the first few days of incubation. On continued incubation the rate of uptake/cell decreased.
In the sea phytoplankters may contribute a major portion of the amount of dissolved vitamins.