A coral reef in the Red Sea, north of the port city of Nuweiba (Egypt), September 2, 2023. KHALED DESOUKI / AFP
Their decline is primarily associated with warming oceans, but there are other pressures on corals as well. In a report published on Monday, September 18, the National Agency for Food, Environment and Occupational Health (ANSES) made the first attempt to assess the chemical risk to these organisms, whose calcareous skeletons form reefs that form a large harbor part of the ocean’s biodiversity.
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In collaboration with the French Office of Biodiversity and the PatriNat department (Center for Expertise and Data on Natural Heritage), ANSES experts worked for more than four years to identify about twenty chemical substances and heavy metals that pose a risk to corals in Guadeloupe, Martinique , represent , Mayotte and Réunion. But the data is scarce and the agency insists the number of risky substances identified in its report is “very likely underestimated.”
It is crucial to relieve corals from the added pressure of ocean warming and acidification, both caused by carbon dioxide emissions. Today, according to the United Nations, 20% of the world’s coral reefs have been destroyed beyond repair in recent decades and only a third of them are considered to be in good condition. About 10% of these fragile ecosystems are located on French territory, in the overseas departments.
Rare works
As a first step, the experts searched the scientific literature to identify around a hundred potentially dangerous substances for corals: hydrocarbons, heavy metals, pesticides, pharmaceutical molecules, microplastics, UV filters (used in sunscreens) and a variety of products for different uses ( cleaning agents, nanomaterials, etc.). The authors then carried out careful work to determine the toxicity thresholds for each identified substance.
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“To estimate these thresholds, we tried to identify the negative effects of these substances on the photosynthesis of algae in symbiosis with corals, on their mortality, their growth, their fertility, etc.,” explains Karen Burga (Anses). Specialist coordinator. Once these thresholds were established, we compared them with data from monitoring measurements in the marine environment. » Overall, the risks could only be estimated for half of the approximately hundred potentially dangerous substances identified. For the other half, the risks remain unknown, particularly due to a lack of monitoring data. In particular, experts point out that such data is missing in certain areas such as Wallis and Futuna or even Saint-Barthélémy.
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