Coral (representational image)
Human activity is changing coral reefs in ways that go far beyond what we can see on the surface. A new study by researchers at the University of Hawaii at Manoa shows that the chemicals we release into the environment actually become part of coral tissue itself, weakening the reef’s ability to cope with heat and ocean acidification.The team found 25 different pollutants from agricultural, industrial and pharmaceutical sources embedded in the soft tissue of coral reefs around the Hawaiian island of Maui. Meanwhile, in areas most affected by human activity, coral reefs had lower energy and nutrient reserves, making them significantly less resilient to environmental stresses.
Looking inside coral tissue: metabolism
Every coral contains a complex mixture of small molecules within its tissues: things like nutrients, energy compounds, stress chemicals, and pollutants.
This assembly is called metabolism.The researchers, led by biologist Zach Quinlan of the Hawaii Institute of Marine Biology, set out to see if these internal chemical signatures could tell a story about human impacts. They examined the metabolism of 380 corals, focusing on two common reef-building species: lobe coral (Porites lobata) and rice coral (Montipora capitata).Samples were collected from 16 sites off West and South Maui, ranging from less disturbed areas to places strongly affected by land use, runoff, and coastal activity.
What they found was startling: Where human influence was strongest, through nearby agriculture, urban areas, sanitation, or other activities, the composition of metabolites in the coral changed significantly. Pollutants accumulated, while internal “banks” of nutrients and energy declined.Quinlan summed up the importance: Monitoring coral metabolites could become a powerful tool for tracking the hidden impacts of human disturbances on marine life.
Different corals, same disturbing pattern
Representative image
One of the surprises in the study was how similar the responses of the two coral species were.Lobe corals and rice corals have very different life strategies: they grow in slightly different ways, occupy different microhabitats, and often respond differently to environmental change. Scientists don’t usually expect pollutants to accumulate or react to stress in quite the same way.However, in this case, both species showed almost identical trends: where human activities were more intense, both had higher amounts of pollutants in their tissues.
Both showed decreased nutrient and energy reserves. Quinlan described this as evidence of how powerful human pressures can be: they can transcend differences between species and push very different coral reefs into similar patterns of decline.
Lessons learned from the 2016 bleaching event
To understand how these chemical changes relate to real-world coral health, the researchers looked at historical data from five of their study sites. They studied how coral cover changed after the major bleaching event of 2016, when unusually warm waters caused widespread stress and bleaching of coral reefs around Hawaii and beyond.A clear relationship emerged: the sites that suffered the most severe declines in coral cover after 2016 also had the most changed metabolites in the new study. At these severely affected sites, corals showed reduced nitrogen and energy reserves, and higher levels of stress-related chemicals in their tissues.In other words, metabolic patterns were not just abstract laboratory data; They have lined up with real losses on the reef.
Corals carrying more pollutants and fewer internal reserves were less able to survive and recover after heat stress.
There are two ways human activity weakens coral resilience
Based on their findings, the team proposed two main mechanisms by which human activities could erode coral resilience:Accumulation of human-made molecules in coral tissuePollutants from agriculture, industry and pharmaceuticals – such as pesticides, fertilizers, drug residues and chemical byproducts – seep into coastal waters and accumulate within coral tissue.
These foreign molecules can interfere with normal cellular functions, stress responses, and energy use.Constant pressure depletes the coral of energy and nutrientsLiving in a polluted or highly disturbed environment forces corals to spend more of their limited nitrogen and energy reserves on coping with stress: repairing damage, dealing with harmful molecules, and maintaining essential functions under stress. Over time, this leaves them less able to respond when exposed to additional stressors, such as higher temperatures or more acidic water.“This response to anthropogenic stress makes corals less resilient to stressors,” Quinlan explained, according to a report by Phys.org. The study suggests a direct link between human disturbance, the accumulation of pollutants in coral reefs, and coral health, and this link appears to be consistent across species.
Metabolites as an early warning system
One of the most promising ideas from the research is the use of metabolites as an early warning system for coral reef health.Instead of waiting for corals to visibly bleach or die, scientists can track changes in pollutant loads, nutrient reserves, energy-related molecules, and stress chemicals within the tissues of corals and other species on the seafloor.
Shifts in these internal features can reveal growing problems even when the reef looks relatively normal from the outside.Megan Donahue, the study’s senior author and director of the Hawaii Marine Biology Institute, emphasized the broader impacts: Many human-made pollutants seep into marine ecosystems, and their combined impacts undermine the resilience of coastal habitats.
Why this is important for coral reefs and for people
This research adds to a growing body of evidence suggesting that coral reefs are being hit from multiple directions simultaneously.
Climate change is bringing warmer, more acidic waters; Local pollution introduces excess chemicals, sediments and nutrients; Human activities on land and in the ocean increase stress and reduce recovery time.When coral reefs have already exhausted their internal reserves and are bearing the burden of pollutants, they become more vulnerable to bleaching, disease and death. This in turn affects countless species that depend on coral reefs, such as fish, invertebrates and algae, and human communities that depend on coral reefs for food, tourism, coastal protection and cultural values.The study underscores an urgent message: to protect marine and human health, we need to reduce the flow of harmful chemicals and stressors into coastal environments, not just focus on global climate drivers.Looking to the future, Quinlan and his colleagues are now exploring whether they can boost nitrogen and energy reserves in coral tissue under controlled conditions. If increasing these reserves makes coral reefs more resilient to heat and acidification, it could point to new strategies for supporting coral reef survival in a changing world.Thinking about all of this, what aspect is most important to you: the invisible buildup of pollutants within coral tissue, or the way these chemical changes occur? To erode coral reefs’ ability to withstand future heat and acid stress?Human activities are fundamentally changing the chemical composition of coral reefs, according to a study conducted by the University of Hawaii at Manoa and published in the journal Nature Communications.
The research team discovered that 25 pollutants from agricultural, industrial and pharmaceutical sources accumulated in the soft tissue of coral reefs around the island of Maui in Hawaii. Additionally, in areas affected by human activities, the availability of energy and nutrients within coral tissue decreases, making coral reefs significantly less resilient to environmental stressors such as warmer or more acidic waters.“Our findings suggest that monitoring a group of chemicals within coral tissue, called metabolites, could serve as a powerful tool for tracking the hidden impacts of anthropogenic disturbances on marine life,” said Zach Quinlan, lead author and a research biologist at the Hawaii Marine Biology Institute in the UH Manoa College of Ocean and Earth Sciences and Technology, according to the report.Quinlan and an international team of researchers tested the metabolomes of 380 lobe corals (Porites lobata) and rice corals (Montipora capitata) from 16 sites off West and South Maui.They found that human activities, both within adjacent watersheds and in the marine ecosystem, changed the composition of coral metabolites. In areas with greater ecosystem disturbance, pollutants have accumulated and nutrient and energy reserves in coral tissue have declined.“It was very surprising that the metabolic processes of both coral species had almost identical trends,” Quinlan said. “These corals have very different life strategies, and we would not normally expect them to accumulate pollutants or respond similarly to disturbances. This shows how powerful these anthropogenic activities really are.”
Evidence from the 2016 bleaching event
Using historical trends in coral cover from five of the sites they sampled, the team found that the sites that experienced the steepest declines in coral cover after the 2016 bleaching event also had the most affected metabolites.
In the most affected sites, nitrogen and energy reserves were reduced, while stress chemicals were enriched.The research team proposed two possible mechanisms through which human activities and pollution of marine environments lead to decreased coral resilience: First, the accumulation of anthropogenic molecules such as pharmaceuticals and industrial by-products, which has increased stress from human activities, requiring coral reefs to use portions of their nitrogen and energy reserves.“This response to human pressures makes corals less resilient to stressors,” Quinlan said. “Together, our findings suggest a direct relationship between anthropogenic disturbance, the accumulation of hazardous pollutants within coral reefs and coral health, which is consistent across species.”Second, pollutants are tracked through the ecosystem. Researchers suggest that monitoring the metabolism of corals or other species on the coastal seafloor could be a powerful tool for tracking human impacts on natural ecosystems.“Beyond the implications for coral health and resilience, this study demonstrates how many anthropogenic pollutants are seeping into marine ecosystems,” said Megan Donahue, senior author of the paper and director of HIMB. “We see increasing evidence that anthropogenic pollutants are having widespread cumulative impacts, undermining the resilience of coastal ecosystems.”This study highlights the urgent need to reduce human impacts on the marine environment to protect marine and human health. Looking to the future, Quinlan and the team are looking at ways to enrich coral tissue nitrogen and energy reserves in controlled experiments to determine whether these increases lead to more resilient corals.
