Running Aground in Paradise: Community Differentiation as Plankton in the Nutrient Limited Open Ocean Encounter Coral Reefs.

Craig Nelson, University of Hawaiʻi at Mānoa, School of Ocean and Earth Science and Technology, Honolulu, HI, United States, James L Hench, Duke University, Nicholas School of the Environment, Beaufort, NC, United States, Jacqueline Comstock, University of California Santa Barbara, Ecology, Evolution, and Marine Biology, Santa Barbara, CA, United States, Craig A Carlson, University of California Santa Barbara, Marine Science Institute/Department of Ecology, Evolution and Marine Biology, Santa Barbara, CA, United States, Kristina Remple, University of Hawaii at Manoa, Oceanography, Honolulu, HI, United States, Anna James, University of California at Santa Barbara, Marine Science, Santa Barbara, CA, United States, Libe Washburn, Marine Science Institute, Santa Barbara, CA, United States and Alice L Alldredge, University of California Santa Barbara, Santa Barbara, CA, United States
Productive coral reefs rise from the ultra-oligotrophic waters of the surface tropical oceans and are continually flushed with oceanic bacterioplankton, yet they foster a distinct microbial community hypothesized to be characteristic of reef ecosystems. Describing the unique characteristics of bacterioplankton in reef waters is important for understanding reef metabolism and productivity but differentiating these communities from the surrounding ocean requires spatially distributed coincident measurement of metagenomics, biogeochemistry and nearshore physics. We conducted a high-resolution synoptic oceanographic profile survey of the offshore and nearshore reef waters surrounding Mo’orea, French Polynesia to couple amplicon-based microbial community surveys with a suite of biogeochemical measurements, physical oceanographic parameters and detailed bathymetric mapping. We document consistently significant differences of several microbial ecotypes among forereef, backreef, reef passes and offshore surface waters, characterizing the key taxa that define the reef planktonic microbiome. By sampling the circumference of the island, we captured offshore to onshore changes across a gradient of wave energy regimes; using unidirectional flow across the reef we estimate the rates of microbial inputs and removals maintaining the unique signature of nearshore habitats, with implications for coral reef microbial and ecosystem processes.