UC Santa Barbara

Marine microbes drive ocean biogeochemistry. The myriad of marine microbes are organized by which microbes respond to an environmental condition and which one are deterred or displaced by a set of environmental conditions. Environmental conditions such as presence or absence of light, concentration of limiting inorganic nutrients and the quantity and quality of bioavailable organic matter are examples of factors that can influence microbial community structure. My work used amplicon sequencing of the 16S rRNA gene a biological tracer to elucidate drivers of biogeochemical trends across coastal and open-ocean environments. In coral reefs, intense recycling of nutrients and organic matter supports highly productive coral reef systems despite being bathed in unproductive oligotrophic waters. Around the French Polynesian islands of Mo’orea and Tahiti, we combined 16S rRNA metabarcoding with a suite of biogeochemical measurements to resolve the origins and spatial influence of an Island Mass Effect, the observed enhancement in primary production surrounding coral reef atolls and islands. Additionally, within the Mo’orea coral reef system we characterized these unique reef microbial communities across a variety of physical regimes and reef habitats, linking bacterioplankton to gradients in biogeochemistry, physical wave forcing, and organic matter composition. Transitioning to open-ocean systems, we applied these methods at the Bermuda Atlantic Time-series site (BATS), one of the most well-studied sites in the global ocean. In open-ocean systems, particulate organic matter (POM) formed in the ocean’s surface plays a central role in the carbon cycle, with sinking POM acting as the dominant pathway in the biological carbon pump. We aimed to better resolve patterns of particle colonization and chemical transformation across depth and particle size, resolving drivers of organic particle attenuation and transformation as organic matter travels from the surface into the deep. Through this research, we utilize microbial community composition as a tracer to inform the origins of observed biogeochemical patterns and organic matter transformation in both coastal and open-ocean environments.