Unpicking the Chemistry of Coral

Coral reefs are one of the most productive, biologically diverse, and economically valuable ecosystems on earth, but our understanding of their chemistry is limited. The plants and animals that make up these complex seafloor habitats release various substances, from macromolecules to individual amino acids. We know that the extracellular dissolved organic matter released by primary producers on the reef plays a key role in fueling the food web and regulating ecosystem function—and also that the matter released varies by species.¹ But coral ecosystems are in decline due to climate change, natural disturbances, disease, and anthropogenic factors, and this drives changes in their composition and outputs.

With 13.5% of corals lost globally in the past decade,² new methods are needed to monitor reefs and support better scientific understanding and conservation approaches. If we can isolate these chemical clues, then they could be used to identify specific populations—or even as markers of the reef’s health.

Reef status and health are usually characterized with diver-based surveys or satellite data, but there is a need for advanced, standardized, and automated techniques to capture their complex nature.² Traditional sampling methods concentrate and separate compounds from the water, but miss many important compounds, and those present in very low quantities, leaving gaps in our understanding. In particular, small, polar molecules—which form the majority components of labile dissolved organic carbon—are often poorly captured. But a team working at the Woods Hole Oceanographic Institution in the United States has tested a new technique that modifies dissolved metabolites so that they cannot slip through the net.³

The researchers attached a benzoyl functional group to dissolved amine- and alcohol-containing metabolites in water samples from coral reefs before assessing their composition and concentration with liquid chromatography-mass spectrometry. Incredibly, this allowed them to identify 23 new metabolites, many of which were linked to photosynthesis and growth. When the team looked more closely, these chemical signatures were associated with particular features or processes happening on the reef. For example, the presence of diseased coral, macroalgae, or crustose coralline algae had the greatest influence on metabolite composition.

Results differed between individual reefs and across bays, but some compounds were consistently high at all locations, suggesting they could be used as a marker of the presence of coral and associated organisms. This included 2,3-dihydroxypropane-1-sulfonate – an organosulfonic acid that is emerging as an important chemical link between marine phytoplankton and bacteria.

This builds on the group’s previous exploration of pre-extraction benzoyl chloride derivatization.⁴ In the earlier work, metabolites were derivatized with benzoyl chloride by their primary and secondary amine and alcohol functionalities and quantified using stable isotope-labeled internal standards produced from 13C6-labeled benzoyl chloride. This allowed them to detect and quantify targeted dissolved metabolites in seawater and saline culture media.

The new study, published in Journal of Proteome Research, successfully demonstrates how to collect previously overlooked, ecologically relevant compounds from coral reefs.² The dissolved metabolites in aquatic environments link organisms across trophic levels, as well as between spatial and temporal scales—becoming, as the authors note, "invaluable chemical currencies."⁴ Methods to read these signatures could uncover the dynamics of baseline biogeochemical cycles in complex marine environments, and help to monitor fragile ecosystems for signs of change related to local and global stressors.

References

1. Moran, M. A. et al. Microbial Metabolites in the Marine Carbon Cycle. Nat. Microbiol. 2022, 7 (4), 508–523.
2. Apprill, A. et al. Toward a New Era of Coral Reef Monitoring. Environ. Sci. Technol. 2023, 57, 13, 5117–5124.
3. Garcia, B. M. et al. Benzoyl Chloride Derivatization Advances the Quantification of Dissolved Polar Metabolites on Coral Reefs. J. Proteome Res. 2024, 23, 6, 2041–2053.
4. Widner, B. et al. Quantification of Amine- and Alcohol-Containing Metabolites in Saline Samples Using Pre-extraction Benzoyl Chloride Derivatization and Ultrahigh Performance Liquid Chromatography Tandem Mass Spectrometry (UHPLC MS/MS). Anal. Chem. 2021, 93, 11, 4809–4817.