Ocean currents promote rare species diversity in protists

Oceans host communities of plankton composed of a huge number of rare species that, as estimated in metagenomic studies, decay as a steep power law of their abundance. We propose that the way oceanic currents limit protists dispersal is a key factor of such biodiversity pattern. We introduce a spatially explicit coalescence model able to reconstruct species ancestry and diversity in the presence of currents. Our model predicts a steep power law decay of the species abundance distribution and a steep increase of the number of observed species with sample size. Metagenomic studies of planktonic protist communities show excellent agreement with our results.