At a global scale, bacteria play a major role in the ecology, functioning, and ecosystem services of the oceans. Nonetheless, detailed knowledge of how humans impact the distributions and biodiversity of bacteria at this scale remains unknown. While extensive data are available on human impacts, information on the distribution of bacterial biodiversity is lacking. To address this need, we compiled a global data set of publicly available 16S rDNA sequences sampled from marine surface waters and assessed the bacterial operational taxonomic units present at each sampling location. Using species distribution modeling, we then combined this information with remote environmental data to map bacterial alpha and beta-diversity patterns at a global scale. We used these maps to assess how human impacts and bacterial biodiversity are associated across the world ocean.
Results/Conclusions
Our maps indicate that hotspots of bacterial alpha-diversity cluster within the tropics, but occur at different locations from many hotspots of macroorganism alpha-diversity. Human impacts and bacterial alpha-diversity are positively correlated, and human impacts are disproportionately high within hotspots of bacterial alpha-diversity. Of the human impacts that we considered, ocean acidification and sea surface temperature change are particularly high in hotspots of bacterial alpha-diversity. Beta-diversity does not correlate with human impacts, but dissimilarity modeling using it indicates that bacterial communities are unique within the regions of the world ocean that are highly impacted by humans. These findings provide the first global picture of the association between human impacts and bacterial biodiversity in the ocean, and they suggest that at a global scale, marine bacterial biodiversity is either promoted by human impacts, or concentrated in the regions of the ocean that are most threatened.