Dispersal, eddies, and the diversity of marine phytoplankton

Lay Abstract Phytoplankton are the “plants” of the ocean; they fix carbon dioxide from the atmosphere and make up the base of the oceanic food chain. Phytoplankton are incredibly diverse, but the reason for their high biodiversity is not well understood. Generally speaking, phytoplankton might be present in a given location either because they are “happy” and able to grow there, or if they are unable to grow there, because they have been transported in from elsewhere (i.e., via dispersal). Previous studies have suggested that “hotspots” of high phytoplankton diversity found in the most dynamic oceanic regions can be explained by dispersal. We explored this question by using a set of computer simulations of phytoplankton ecology coupled to a realistic ocean circulation. We show that dispersal can only partly explain diversity hotspots. The mixing of populations by ocean currents and eddies is important, but a plentiful supply of nutrients and variable environmental conditions also enhance phytoplankton diversity. This work has generated hypotheses that will stimulate new projects to test them in the field.