Corals Could Help Scientists Track Marine Pollution Over Time, Study Finds

Coral reefs may offer scientists a new way to monitor pollution in coastal waters, with research showing that coral tissues retain chemical traces of human activities over time. A study published in Nature Communications identified 25 contaminants in corals collected from reef sites around Maui, Hawaii, including substances associated with cosmetics, medicines and agricultural runoff. The researchers found higher contaminant levels at sites exposed to greater human influence. By analysing the small molecules in coral tissues, scientists were able to distinguish reefs according to their levels of human disturbance, suggesting that the technique could help monitor pollution and assess coral health beyond what conventional water sampling reveals.

Coral tissues reveal pollution linked to human activity

The research team collected 380 samples from two coral species, lobe coral (Porites lobata) and rice coral (Montipora capitata), across 16 reef sites along approximately 70 kilometres of Maui’s coastline. The samples were analysed using metabolomics, a technique that examines small molecules such as sugars, lipids and amino acids in living organisms. Changes in these chemical profiles can reveal how organisms respond to environmental conditions and stress.

The researchers identified three broad groups of reef sites based on the chemical profiles of the corals. These groups corresponded to low, medium and high levels of human influence, matching existing information on land-use disturbance and water samples collected at the sites. Reefs exposed to greater human activity showed higher levels of contaminants, while three of the five sites in the most heavily influenced group were located near wastewater treatment plants. The similar patterns observed in both coral species suggested that human activities were leaving a measurable chemical imprint on the reefs.

Why coral monitoring could offer a longer-term picture

Traditional water sampling can identify pollutants present at a particular place and time, but it may not capture the full history of contamination affecting a reef. Coral tissue, by contrast, can contain contaminants that have accumulated over time, potentially offering a broader picture of the environmental pressures experienced by these organisms. Because corals cannot move away from polluted areas, their chemical composition may help researchers identify locations where human activities are placing greater pressure on marine ecosystems.

The approach could eventually support reef monitoring and provide an early warning of environmental stress. However, it has practical limitations. The specialised equipment needed for chemical analysis is expensive and may be difficult to access in countries with extensive coral reefs. Collecting samples has also traditionally involved removing small pieces of coral tissue and skeleton using tools such as a hammer and chisel. Researchers are now developing less invasive sampling methods that use a needle to collect smaller samples, allowing corals to recover more quickly. These developments could make the technique more practical for routine monitoring, although its wider application will depend on the cost and availability of laboratory analysis.

Pollution may leave coral reefs less resilient to ocean warming

The study also explored whether the chemical health of corals was associated with their ability to withstand rising ocean temperatures. Researchers compared their findings with the effects of a marine heatwave in 2015 and 2016, which caused coral die-offs in Maui and other locations. They found that sites with healthier coral metabolomes generally retained more coral cover, raising the possibility that reefs under less pressure from local pollution may be better able to withstand heat stress.

However, the researchers stressed that this relationship was not conclusive. Long-term coral-cover data were available for only five of the 16 sites, and the coral samples used to assess chemical health were collected in 2018, after the heatwave. The team therefore could not establish what the pollution levels had been before the event or determine whether healthier coral chemistry directly contributed to greater survival.

The findings highlight the need to consider local pollution alongside broader threats such as ocean warming. Rising sea temperatures can trigger mass coral bleaching, while wastewater, agricultural runoff and other pollutants place additional pressure on reef ecosystems. Metabolomics could help scientists identify reefs facing multiple stressors and guide conservation efforts towards vulnerable sites. Further research will be needed to establish how reliably the method can track changes in coral health, but the study suggests that monitoring the chemistry of corals could become a valuable tool for understanding and protecting reefs in a warming world.

References:

https://www.nature.com/articles/s41467-026-74960-7

Corals keep a record of pollution, pointing to a new monitoring method: Study

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