Consistent marine biogeographic boundaries across the tree of life despite centuries of human impacts

Over millennia ecological and evolutionary mechanisms have shaped macroecological distributions across the tree of life. Research describing patterns of regional and global biogeography has traditionally focussed on the study of conspicuous species. Consequently, there is limited understanding of cross-phyla biogeographical structuring, and an escalating need to understand the macroecology of macrobial and microbial life. Here we used environmental DNA metabarcoding to explore the biodiversity of marine metazoans, micro-eukaryotes and prokaryotes along an extensive and highly heterogeneous coastline. We expected environmental forces to be responsible for creating similar biogeographical assemblages across kingdoms of life, while life-history strategies and pervasive anthropogenic impacts were predicted to disturb such patterns. We found that despite centuries of significant human activities, biogeographic patterns were consistent across kingdoms, underpinned primarily by abiotic factors. Our work highlights the importance of studying multiple domains of life to understand the maintenance of biodiversity and potential drivers of future change.