Ubiquitous abundance distribution of non-dominant plankton across the world’s ocean

Species Abundance Distributions (SADs) bear the imprint of ecological processes that shape biological communities, and are therefore used to discriminate among different scenarios of community assembly. Even though empirical distributions appear to follow a handful of qualitative laws, it is still unclear if and how quantitative variation in SADs reflects peculiar features of the communities and their environmental context. Here, we use the extensive dataset generated by the Tara Oceans expedition for marine microbial eukaryotes (protists) and an adaptive algorithm to explore how SADs vary across plankton communities in the global ocean. We show that the decay in abundance of non-dominant OTUs, comprising over 99% of local richness, is commonly governed by a power-law. The power-law exponent varies by less than 10% across locations and shows no biogeographical signature, but is weakly modulated by cell size. Our findings suggest that large-scale ubiquitous ecological processes govern the assembly of non-dominant plankton throughout the global ocean.