Seawater samples may offer early clues to changing reef health
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Doctors can often detect diseases in humans using minimally invasive methods, like blood or urine tests, before symptoms become severe. Now, researchers at the Woods Hole Oceanographic Institution (WHOI) are applying a similar concept to coral reefs, showing that the water surrounding reefs contains chemical and microbial signals that could reveal changes in ecosystem health long before those changes are visible.
In a new study published in The ISME Journal, WHOI scientists combine chemistry, biology and ocean physics to examine how dissolved molecules, microorganisms and water movement interact across coral reefs and a nearby seagrass meadow in the U.S. Virgin Islands. The findings show that each sample site has its own distinct chemical and microbial signature and that ocean currents play a major role in shaping those patterns on timescales as short as a few hours.
"Coral reefs are incredibly dynamic ecosystems," said Amy Apprill, a co-author of the study in WHOI's Marine Chemistry and Geochemistry Department and inaugural director of the WHOI Schiller Center for Reef Solutions. "When we first looked at the data, some of the patterns didn't make sense. Bringing ocean physics into the study helped explain how water movement was shaping the chemistry and microbes at each reef. That kind of interdisciplinary approach gives us a much more complete picture of reef health."
Researchers collected seawater from two neighboring coral reefs and a nearby seagrass meadow over four days, sampling at dawn and midday. They measured dissolved compounds known as metabolites, or small molecules produced and consumed by marine organisms, alongside microbial communities. They combined those data with a high-resolution computer model that tracked where the water had traveled before reaching each site and how and when it traveled between the sites.
Nearby sites, different signatures
Although the sites were separated by less than a quarter mile (less than 0.4 kilometer), they behaved very differently. The sheltered seagrass meadow maintained relatively stable water conditions and accumulated a unique suite of dissolved compounds, while one reef experienced a daily influx of offshore water that reshaped both its chemistry and microbial community.
"If you don't understand the physics of how water moves through a coastal ecosystem, you're missing a huge part of the story," said Elizabeth Kujawinski, a senior scientist at WHOI and a co-author of the study. "The chemistry and microbes in seawater provide a snapshot of everything happening within the reef. By combining those measurements with computer-generated ocean circulation, we're beginning to understand the hidden processes that drive ecosystem health."
The study leverages a chemical-tagging method developed at WHOI that allows researchers to quantify the composition of biologically available small molecules released by marine microorganisms. Originally used to better understand ocean chemistry, the technique is now helping researchers identify potential indicators of reef condition and ecosystem change.
Borrowing tools from medicine
The study's lead author, Brianna Garcia, a postdoctoral investigator in WHOI's Marine Chemistry and Geochemistry Department, says the project illustrates the value of bringing expertise from outside traditional coral reef science to tackle complex environmental questions.
Garcia joined WHOI with a background in analytical chemistry and human health, where researchers use chemical markers in blood and other samples to diagnose disease. She saw an opportunity to apply similar approaches to marine ecosystems.
"In human medicine, we use minimally invasive tests to look for early warning signs of disease," Garcia said. "We're beginning to think about reef water in much the same way. Instead of waiting until corals show obvious signs of stress, we can look for subtle chemical and microbial changes in the surrounding water that may signal that something is changing. It's an exciting example of how ideas from human health research can help us better understand, and eventually protect, ocean ecosystems."
Building a baseline for reef change
More work is needed before these measurements can become routine monitoring tools, but the consistency of the chemical and microbial patterns observed over several days suggests they may provide a reliable baseline against which future disturbances, such as disease outbreaks, pollution or heat stress, could be detected.
The study showcases the interdisciplinary research approach that the newly launched WHOI Schiller Center for Reef Solutions will bring to threatened coral reef ecosystems. By combining expertise in analytical chemistry and ocean physics, researchers were able to develop a more complete picture of reef health than any one field could provide on its own.
"Healthy coral reefs are essential to both ocean life and the people who depend on them," said Apprill. "Meeting the challenges they face requires bold thinking across disciplines. The Schiller Center creates opportunities for scientists and engineers to pursue high-risk, high-reward research that can lead to entirely new approaches for protecting and restoring reefs."
Publication details
Brianna M Garcia et al, Spatiotemporal and hydrodynamic influences on microbial and exometabolite dynamics in coral reef and seagrass ecosystems, The ISME Journal (2026). DOI: 10.1093/ismejo/wrag177
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Citation: Seawater samples may offer early clues to changing reef health (2026, July 27) retrieved 28 July 2026 from https://phys.org/news/2026-07-seawater-samples-early-clues-reef.html
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