Protists Exhibit Stronger and More Recent Oceanic Genetic Structure than Archaeplastida and Metazoa

The global distribution of biodiversity is shaped by a complex interplay of evolutionary history and ecological processes. While biogeographic patterns are well defined for animals and plants, the global distributions of protists remain unclear. A key question is whether protists follow the same broad biogeographic principles as macroscopic life. To address this, we compiled 88 marine COI metabarcoding studies performing population-genetic analyses across ocean basins. Our results reveal that most protist phyla exhibit pronounced genetic structure among oceans, a pattern exceeding that reported for Archaeplastida and Metazoa. This likely reflects recent, and potentially human-mediated, introductions, influencing protist dispersal and contemporary community assembly. By demonstrating that protist distributions are not historically cosmopolitan, our study supports the existence of common eukaryotic biogeographic patterns that transcend organismal size.