The biodiversity and biogeography of Prochlorococcus, the dominant photosynthetic microbe in a globally changing ocean
Zackary I. Johnson, Duke University Marine Lab Beaufort, NC USA

Microbes (single celled organisms) are the dominant form of life in the global ocean and drive most of the energy production (and use), ecology and elemental transformations. However, global climate change is expected to modify the environment of these unique life forms with likely consequences for their abundance and biodiversity. Here I use a model marine microbe to describe the patterns and extent of marine microbial biodiversity and biogeography and predict how this may shift with global climate change. The marine cyanobacteria Prochlorococcus is the most abundant photosynthetic microbe in tropical and subtropical open oceans and accounts for 5-25% of global marine photosynthesis. This genus is comprised of two major subgroups, one that is high-light adapted and numerically dominant near the surface and a second clade that is low-light adapted and numerically dominant deeper in the sunlit zone. However, using advanced sequencing technologies we can now distinguish numerous genetically distinct clades that have unique environmental distributions. Here I report on the biodiversity and distribution of these groups and their unique contribution to marine ecology and biogeochemistry over vast regions of the Pacific and Atlantic Oceans. Using models of global climate change, I show that the distribution and biodiversity of these microbes is expected to change substantially in the future with implications for the functioning of these ecosystems. These results highlight the importance of microbial biodiversity and how it can be used to predict and document changes in global biodiversity in response to a changing global ocean.

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