How do coral chemical compounds affect reef composition and health?

Finding a new source of underwater caffeine was just an added bonus from a new study examining the effects of chemical compounds corals release into seawater.

The study found that the organic chemical compounds produced by metabolism — known as metabolites, or exudates — vary significantly across coral species, and that the compounds affect the abundance and composition of reef microorganisms differently.

This differential release of metabolites from benthic reef organisms is particularly important in the Caribbean, where coral dominance is shifting from hard stony corals to soft octocorals in response to human-induced stressors such as eutrophication, overfishing and global climate change.

The study “shows the importance of benthic exudates in shaping microbial communities on oligotrophic reefs by focusing on the exudates released from abundant hard corals, octocorals and an invasive alga,” according to the authors of the Woods Hole Oceanographic Institution (WHOI)-led article ), “Benthic exometabolites and their ecological importance for threatened Caribbean coral reefs”, published in ISME Communications.

“We wanted to know what molecules coral organisms release into the environment and how those molecules affect reef microbes in the seawater surrounding the corals,” said lead author Laura Weber, a former postdoc and current information systems collaborator at WHOI’s Department of Marine Chemistry and Geochemistry.

“As the species composition of these reefs shifts, the chemicals that are released onto the reef are likely to change, which will then have an impact on the microbial community,” Weber said. “We need to pay more attention to how changes in reef structure and species composition might affect the microbes that live on the reef, leading to more feedbacks in terms of reef health.” She said that understanding microbes on reefs like them function and how they might contribute to the health of corals and reefs themselves, “is quite an untapped area to explore”.

Here’s the caffeine connection.

For the study, the researchers collected exudates from six species of Caribbean benthic organisms in a laboratory setting using organisms from the Virgin Islands National Park, including stony corals, octocorals and an invasive crustal alga called Ramicrusta textilis. The researchers found this surprising R. textiles released caffeine in large quantities.

Their results “further demonstrate that exudates from benthic organisms contribute to the complex pool of extracellular metabolites in reef seawater, and that exudate composition varies significantly by species,” the study states

why R. textiles Produces caffeine, the study notes that caffeine production has not been extensively studied for marine organisms, but that it is a common metabolite produced by terrestrial plants in general to deter herbivores and pathogenic microbes. These traits “might contribute to the ability R. textiles to invade and thrive on Caribbean reefs,” the report said. “Given the growing prevalence of Ramicrusta follow-up research is needed on various Caribbean reefs examining the ecological importance of its metabolites on microbes and other reef organisms.”

This study “is an important step forward in identifying chemical signals that can help scientists assess reef health,” said Elizabeth Kujawinski, co-author of the paper. “Similar to human health diagnostics, the chemical signals within a reef ecosystem are intimately linked to the functions of symbiotic relationships within reefs.” Kujawinski is a senior scientist in WHOI’s Department of Marine Chemistry and Geochemistry and director of the Center for Chemical Currency at one Microbial Planets (C-CoMP), a National Science Foundation Science and Technology Center based at WHOI.

Co-author Amy Apprill, associate scientist in WHOI’s Department of Marine Chemistry and Geochemistry, said an important implication of the research is that a diverse benthic community contributes to a more diverse metabolite pool and likely supports a more diverse microbial community.

“We’re trying to build a kind of library of what microbes and metabolites are present on reefs. My dream is to go out on a reef, take a bucket of reef water, analyze it for microbes and metabolites, and be able to tell something about the health of that ecosystem,” Apprill said. “This is so important because “Current methods of monitoring reefs are heavily visual and it can take months or years to determine if corals are diseased or growing. Metabolites and microbes have the potential to be really sensitive sensors of reef health.”

Relation: Weber L, Soule MK, Longnecker K, et al. Benthic exometabolites and their ecological importance on threatened Caribbean coral reefs. ISME COMMUN. 2022;2(1):1-13. doi: 10.1038/s43705-022-00184-7

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