Award: OCE-1949033

Coral reefs are highly productive and dynamic ecosystems that grow in some of the most resource-poor and dilute waters on the planet. The acquisition of nutrients and the retention and recycling of those nutrients within the system is crucial to their survival, and many of these processes are governed by microbial interactions. The overall goal of this project was to understand the role of microbial communities and the dissolved organic matter they use as their primary food resources in coral reef ecosystems. Intellectual Merit: The first goal of this project was to understand day and night cycling of the chemistry and microbiology of the reefs. To this end we developed new methods of collecting water samples every few hours in various reef environments by working with several labs to design and deploy autosamplers. Across 3 major field campaigns in Moorea and Curacao we collected and processed more than 200 water samples and analyzed them for the chemical and microbial composition. Ongoing work seeks to understand the rhythms of these processes in the reef using these data and develop models of how microbes interact with water chemistry to acquire and recycle reef nutrients. The second major goal was to better understand the dynamics of microbes and DOM in key coral reef processes, including natural variation in the water and in organisms, but also how these dynamics respond to emerging threats such as nutrient pollution, thermal stress-induced bleaching, and ongoing phase shifts from coral to algal dominance. Building from ongoing collaborations in Moorea, Hawaii and Curacao we published 13 peer-reviewed articles, with 2 more in review, exploring diverse ways that microbes and DOM play key roles in reef ecology and biogeochemistry, including a major review of the topic in Annual Reviews in Marine Science. Two high profile journal articles defined the chemical composition of tissue metabolites and exometabolits of coral reef primary producers in Hawaii and Moorea, respectively. Two more articles explored how bleaching impacts the tissue-associated and water column microbiology of corals during bleaching events in Hawaii and Moorea, respectively. Two articles focused on larval thermal stress, examining how prior heating and the addition of different zooxanthellae symbionts influence their ability to withstand warmer oceans. Two articles developed models of pathogen loading and hypoxia to coral reef waters, both significant threats to the microbial ecology of reefs. And two manuscripts focused on the impacts of nutrients on the microbiology and biogeochmistry of reefs, using both experimental and natural submarine groundwater inputs as test cases. Broader Impacts: This project has made significant contributions to the conservation managment of reefs. This work has contextualized how crucial nutrient recycling processes vary across gradients of coral coverand nutrient availability, two factors highlighted as the main drivers of reef decline in the Anthropocene, making the results useful to managers seeking to enhance ecosystem-based approaches to reef restoration. Ongoing macrolgal phase shifts in the MCR-LTER are hypothesized to be related to nutrient pollution, and this project supported major survey and workshop efforts to understand nutrient cycling in the reefs of Mo'orea. This project has made signficant advances in broadening participation in coral reef science. This grant has supported the work of several students from underrepresented groups in STEM fields, all of which have gone on to further academic careers. Personnel supported by the project included 1 female student, 1 transgender student, and 1 Black student, each of which published a peer-reviewed first-authored manuscript from their work and moved on to funded graduate or postdoctoral programs. Of the 13 peer-reviewed publications emerging from this project 8 were led by female scientists. Finally, this project engaged extensively in outreach and communication programs. Media communication has included articles in popular magazines such as Discover, interviews by NPR, local news engagements, podcasts, and extension engagements with UH Sea Grant. Both students and faculty brought their results to 3 international conferences as well as 3 local conferences in Hawaii where they presented their work to fellow scientists. Last Modified: 11/18/2023 Submitted by: CraigENelson