Postdoctoral Fellowship: OCE-PRF: Investigating the Microbe-Metabolite Interactions that Govern Bacterial Growth Efficiency in Coral Reefs

Coral reefs are among the most diverse and productive ecosystems on the planet, yet they are increasingly threatened by local and global stressors. One major consequence of reef degradation is the shift from coral-dominated ecosystems to algae-dominated ecosystems. These organisms modulate reef water column microbial communities and dissolved organic matter (DOM) substrates. Thus, as the balance of reef communities shift, reef water chemistry and microbiology shift in tandem. In healthy, coral-dominated reefs, microbes in the water column serve as critical regulators of reef ecosystem function, recycling DOM and supporting ecosystem productivity and biomass. As reefs across the globe undergo phase shifts to increased macroalgal dominance, these critical processes are disrupted. This project will uncover the microbial mechanisms that drive these changes by studying how different reef organisms release DOM and how reef microbes process that material. By improving understanding of microbial contributions to reef ecosystem function, this project will support more effective conservation and restoration strategies, ultimately benefiting both biodiversity and human communities that depend on healthy coral reefs. The project will also include a strong education and outreach component, including mentoring students, contributing to a bridge program in marine biogeochemistry, and launching a science-focused podcast and radio series to increase public engagement with marine science.

Microbe-DOM interactions in the water column serve as critical bottom-up regulators of coral reef ecosystem function, with bacterial growth efficiency (BGE) on DOM substrates informing the recycling of exuded primary production and supporting broader ecosystem productivity and biomass. Currently, we lack a mechanistic understanding of how microbe-metabolite interactions might drive BGE in healthy and degraded coral reefs. This proposal will test the broad hypothesis that DOM metabolites released by benthic primary producers in coral reefs select for specific bacterioplankton communities, which in turn yield distinct growth efficiencies based on their central carbon metabolisms and the nutritional content of the selecting substrates. As reefs degrade, shifting dominance of benthic primary producers from corals to algae will thus drive changes in BGE, reef carbon cycling, and broader ecosystem function. The proposed project will combine three interdisciplinary objectives spanning in situ surveys and controlled bottle incubations to address how microbial metabolic capacity and substrate composition underpin BGE in coral reefs. Objective 1 will characterize the carbon metabolism of coral reef bacterioplankton associated with different reef benthic community compositions in situ using untargeted metagenomics. Objective 2 will assess if genomic substrate preferences of in situ bacterial communities are adapted to benthic primary producer exudates using untargeted metabolomics. Lastly, Objective 3 will test the interaction between bacterial communities and DOM substrates on BGE via batch culture incubations using stable-isotope-probing. The proposed project will illuminate the microbial mechanisms that drive coral-algal phase shifts and lead to changes in ecosystem function–critical information for management of and restoration of healthy coral reef ecosystems.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Award Number: 2508485
Principal Investigator: Wesley Sparagon
Funds Obligated: $341,191
State: CA