Award: OCE-2023298

The reactivity of the thousands of largely uncharacterized molecules comprising marine dissolved organic matter (DOM) is a crucial component of global carbon cycling, providing food and energy for microbes living in the ocean and regulating the types and interactions of microbial communities. This project fundamentally sought to develop tools to characterize the chemical composition and microbial transformations of marine DOM, using coral reefs as a coastal study system with complex sources, reactivities and fluxes of labile organic matter and well characterized microbial dynamics. 

Intellectual Merit

This project developed a system for using untargeted tandem mass spectrometry to measure, classify and estimate the fluxes and lability of hundreds of unknown compounds released by various reef organisms, including corals, macroalgae and crustose coralline algae. We released a significant publication in PNAS defining ways to generate, characterize and differentiate freshly exuded DOM from keystone reef taxa from the Moorea Coral Reef Long Term Ecological Research program in French Polynesia. We used this work in three publications to further develop pipelines for handling untargeted exometabolite data, chemoinformatic classification tools and bioinformatic tools that allowed us to understand microbial utilization of these compounds.

Using these methods, we published work that fleshed out the types of microbes that consumed various types of labile DOM released in reef ecosystems, vastly expanding our understanding of the variety of chemical classes that can be metabolized by microbes. In a series of four associated publications we linked the growth of specific microbial taxa with the removal of a vast array of previously uncategorized compounds, including exudates released by corals during a bleaching event in Moorea, sugars and lipids released by corals and algae in Curacao and planktonic communities around Bermuda.

We placed our understanding of the types of labile DOM and key microbial players in reefs into ecological context by exploring the dynamics of both across many coastal ecosystem types. We contributed our data from several ecosystems (Moorea, Hawaiʻi, Curacao) to a major global inventory of xenobiotics in DOM published in Nature Geoscience. In the Moorea Coral Reef LTER system, we demonstrated how specific microbial taxa associated with various reef habitats and how that was linked to coastal biogeochemistry and physics. We developed additional context around sources of DOM to these coral reef systems, including publishing specific explorations of 1) submarine groundwater discharge and 2) terrestrial sources. We also supported three published explorations of microbial-DOM linkages in mangrove, offshore and temperate tidepool ecosystems.

To understand the host-microbial interactions that define and transform the dissolved metabolites released by reef organisms, we produced a series of papers exploring linkages between microbiomes and metabolomes across fishes, corals and algae. We published three papers applying coupled metagenomics and untargeted mass spectrometry to define the key microbial players and metabolites involved in the degradation of macroalgae, using herbivorous fish guts as a model system. Using the Waimea Bay ecosystem in Hawaiʻi for context, we conducted a broad survey to explore linkages between microbiomes and metabolomes across dozens of reef benthic species. To place this work in the context of environmental changes in Hawaiʻi we published three papers in PNAS exploring the microbiomes of corals in context of catchment-scale microbial metacommunity dynamics, during a widespread bleaching event and during a multi-year ocean acidification experiment.

Broader Impacts

This project has made significant contributions to the conservation and management of reefs, including a major Annual Review contextualizing how DOM is central to the health of coral reefs. Ongoing macroalgal phase shifts in the MCR-LTER are hypothesized to be related to terrestrial influence, and this project supported major survey and workshop efforts to understand linkages between DOM, nutrient recycling and land use in the reefs of Mo'orea. This work also supported engagement in local emergencies, including developing tools to monitor petroleum DOM during the Red Hill fuel leak crisis on O‘ahu and monitoring pyrogenic DOM released by the Lahaina Wildfires on Maui.

This project has made significant 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. Three undergraduate theses were supported, including two female kama’aina students and one non-binary student. The work supported one PhD and one international MS thesis, as well as the ongoing work of a kama’aina PhD Candidate finishing next year. Of the more than 20 peer-reviewed publications emerging from this project half 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: 12/29/2025
Modified by: Craig E Nelson