Effects of chemical environmental contaminants on the health and resilience of scleractinian corals

Coral reefs are some of the most diverse and valuable ecosystems on Earth. Although reefs cover less than 2% of the ocean bottom, over 25% of marine life relies on coral reefs for food and shelter. Reefs provide habitat and support biodiversity; globally, half a billion people live within 100 km of a coral reef and benefit from its production and protection. Coral reefs are also one of the world's most threatened resources due to numerous environmental stressors. The effects of global climate change, with associated higher ocean temperatures and acidification, is frequently compounded by the impacts of local stressors and has resulted in significant declines in coral cover worldwide. Specifically, the effects of many chemical contaminants, including metals, insecticides, herbicides, industrial organic chemicals, antifouling chemicals, and hydrocarbons are not well characterized; this represents an important knowledge gap in understanding the potential impacts of these chemicals to coral health and resilience. This paper summarizes the current knowledge on the effects of the main classes of marine chemical pollutants to scleractinian corals and outlines further research needs. Laboratory studies have identified toxicity thresholds for a number of these chemicals, however methods and metrics are inconsistent between studies, and a lack of exposure characterization can result in over or underestimation of toxicity. A broader assessment of pollutant concentrations in the coral reef environment would substantially improve understanding of exposure risk and support the use of environmentally realistic exposures in the laboratory. This would also identify regional contaminants of greatest concern and may elucidate the sub-lethal effects of chronic exposures and potential interactive effects. Filling these critical scientific gaps will significantly improve assessment of current management strategies and support informed management actions targeted at reducing the levels and impacts of chemical pollutants, with the goal of reducing further coral mortality and reef degradation.