Project: The coupling between DOM, algae, and microbes on coral reef platforms

This project is part of the ETBC (Emerging Topics in Biogeochemical Cycles) program.

From NSF award proposal:
The proposed research will investigate the coupling between primary producers and the utilization of dissolved organic matter (DOM) by marine heterotrophic microbes on coral reefs. Previous metagenomic studies of the microbial communities associated with near-pristine and degraded coral reefs demonstrated a shift from a microbial food web similar to the open ocean (Prochlorococcus spp. and SAR11-like bacteria) to a community dominated by "super-heterotrophs", most closely related to known pathogens like E. coli, Staphylococcus spp., Streptococcus spp., Enterobacter spp. and Vibrio spp. This shift is associated with a decline in coral cover and an increase in coral disease prevalence. Our previous research has also shown that dissolved organic carbon (DOC) concentrations are lower on coral reef platforms compared to measurements of offshore waters (60-80 µM). On degraded reefs, we have observed DOC measurements as low as 30 - 40 µM, a value similar to concentrations observed in the deep Pacific Ocean. The observation of low DOC measurements on degraded reefs is decoupled from the high abundance of macroalgae, which one might expect would raise levels of DOC through the release of photosynthate into the water column.

The data generated from the proposed research are key to understanding the microbial, chemical, and ecological dynamics on today’s coral reefs. The proposed research plan will consist of five inter-related objectives that will use a combination of field surveys, molecular characterization (microbes and DOM) and experimental approaches to assess the overall hypothesis. We propose to use a combination of archived samples from previous reef expeditions as well as conduct two field visits to reefs in French Polynesia (Moorea) and the Line Islands (Kiritimati) for focused sampling and experimentation. The biogeochemistry, local physical oceanography, and detailed reef ecology has been well characterized and continues to be monitored as part of the MCR-LTER program at Moorea. This environmental context will be useful in interpreting our experimental and field results at Moorea. We will also compare two field sites, Moorea and Kiritimati to ensure that our results are not specific to one region.