Phytoplankton diversity and community structure affected by oceanic dispersal and mesoscale turbulence

Lay Abstract Phytoplankton are an extremely diverse set of floating, microscopic organisms, which are freely transported by water movements (current, eddies, etc.) and make up the base of the oceanic food web. This work explores how their diversity is affected by dispersal by different scales of motions in the ocean. Previous theoretical studies, based mostly on terrestrial ecosystems, have suggested that the number of phytoplankton types able to coexist at the same location should increase with increasing levels of dispersal. Here we test this hypothesis for a realistic range of oceanic conditions using a set of computer simulations of phytoplankton ecology coupled with a turbulent ocean circulation model. Our results indicate that oceanic communities become dominated by a smaller number of phytoplankton types as dispersal increases, but they have a larger ability for coexistence in larger home range areas. Dispersal due to oceanic eddies contributes significantly to these changes. Moreover, mixing of communities can only partially explain the increase in local coexistence, and we believe that dispersal allows more phytoplankton types to become equally competitive.