Marine phytoplankton play a crucial role in ocean productivity, yet very little is known about the global patterns of diversity of these extremely diverse marine organisms, varying from photosynthesizing cyanobacteria to plant-like diatoms.
Combining more than a million occurrence records from GBIF, OBIS, and others with 10 environmental variables representing key dimensions of phytoplankton ecological niches, authors of this paper modeled the distributions of more than 500 species and globally projected the models onto monthly data fields.
Based on these projections, the authors produced a global phytoplankton map, showing threefold richness in the tropics compared to higher latitudes, confirming metabolic theory, with sea surface temperature as the most important predictor.
In cooler waters, however, richness is lower than expected, with regions between 35 and 60 degrees latitude showing the greatest divergence. The authors suggest that environmental variability may play a role in reducing richness—either directly or through enhancing competitive exclusion.