Metals, pesticides, UV filters and hydrocarbons pose a risk to coral reefs

2023-09-18 00:01:04
A coral reef in the Red Sea, north of the port city of Nuweiba (Egypt), September 2, 2023. KHALED DESOUKI / AFP

Their decline is mainly associated with ocean warming, but there are other pressures on corals. In a report published Monday September 18, the National Agency for Food, Environmental and Occupational Health Safety (ANSES) conducted the first attempt to assess the chemical risk for these organisms whose calcareous skeletons form reefs sheltering a large part of the biodiversity of the oceans.

Read also: In the Antilles, corals under threat of “severe bleaching” and “risk of mortality”

In collaboration with the French Biodiversity Office and the PatriNat unit (Center of expertise and data on natural heritage), ANSES experts worked for more than four years to identify around twenty chemical substances and of heavy metals presenting a risk for corals located in Guadeloupe, Martinique, Mayotte and Reunion. The data is, however, rare and the agency insists that the number of risky substances identified in its expertise is “most likely underestimated”.

Relieving corals from the added pressures of ocean warming and acidification – both caused by carbon dioxide emissions – is crucial. Today, according to figures cited by the United Nations, 20% of the planet’s coral reefs have been irreparably destroyed in recent decades and only a third of them are considered to be in good condition. Around 10% of these fragile ecosystems are located on French territory, in the overseas departments.

Rare works

In a first step, the experts screened the scientific literature to identify around a hundred substances potentially dangerous to corals: hydrocarbons, heavy metals, pesticides, pharmaceutical molecules, microplastics, UV filters (used in sun creams) and a variety of products for various uses (detergents, nanomaterials, etc.). The authors then carried out painstaking work to determine the toxicity thresholds for each identified substance.

Read also: Article reserved for our subscribers The rate of rising oceans, crucial for the survival of coastal ecosystems

“To estimate these thresholds, we sought to identify the negative effects of these substances on the photosynthesis of algae in symbiosis with corals, on the mortality of the latter, their growth, their fertility, etc., explains Karen Burga (Anses), coordinator of the expertise. Once these thresholds were established, we compared them with data from monitoring measurements in the marine environment. » In total, the risks could only be estimated for half of the hundred or so potentially dangerous substances identified. For the other half, due in particular to a lack of monitoring data, the risks remain unknown. In particular, experts note the absence of such data in certain territories such as Wallis and Futuna, or even Saint-Barthélémy.

You have 46.75% of this article left to read. The rest is reserved for subscribers.