Nutrient competition and division synchrony in phytoplankton

In the Gulf Stream in October of 1968, division of at least nine species of dinoflagellates occurred between 03.00 h and 06.00h indicating a high level of developmental synchronization. Whereas light-dark and temperature cycles act independently on each species, the synchronizing agent in the Gulf Stream apparently couples the development of many species of the dinoflagellate community. It is proposed that diurnal fluctuation in nutrients, acting through interspecific competition, is the coupling and synchronizing agent in this environment. A mathematical model of interspecific competition shows that regular, short-term changes in nutrient levels are extremely sffective in synchronizing the development of several species. Calculations also suggest that division eynchrony is an indicator of the occurrence of competition for nutrients and that the degree of synchronization increases with the severity of nutrient limitation on the phytoplankton.