récifs coraliens
Expert assessment
2 min

Coral reefs in the French overseas territories: the impact of chemicals is confirmed

The coral reefs are a part of the ecosystems affected by climate disruption. But what do we know about the impact of chemicals on these reefs? With the support of the French Biodiversity Agency (OFB), ANSES has looked into the health risks of these substances. Of the hundred or so substances identified as potentially toxic to corals, the Agency was able to carry out a risk assessment for around fifty of them, based mainly on data available from Guadeloupe, Martinique, Réunion Island and Mayotte. These include UV filters, hydrocarbons, pesticides and metals. The report shows that half of the substances assessed may present risks for coral reefs and contribute to their degradation. The Agency warns that, in the absence of available data, this number is very likely to be underestimated.

Ecosystems already threatened by the effects of climate change

Coral reefs are home to almost 100,000 species, including molluscs, crustaceans, sponges, fish, rays, turtles and sharks.  Unfortunately, these ecosystems -- among the richest on the planet -- are being seriously threatened.  Worldwide 20% of coral reefs have been irretrievably destroyed in recent decades, and only a third of the remaining coral is thought to be in a satisfactory state.

At the forefront of the threats identified are the consequences of climate disruption, such as the rise in ocean temperatures and acidification, as well as an increase in the number of cyclones. Added to this is the pollution linked to human activities, leading to the presence of numerous chemicals in the oceans. 

France has coral reefs in all three tropical oceans. It is therefore particularly concerned by the protection of these ecosystems in its overseas territories.

The number of toxic substances is probably underestimated

A review of the scientific literature carried out for this assessment by the French Biodiversity Agency (OFB) identified around a hundred chemical substances as potentially toxic to corals. These substances were grouped into categories:

  • hydrocarbons,
  • metals,
  • pesticides,
  • UV filters,
  • microplastics,
  • plant protection products, and
  • an "other substances" category including detergents, preservatives, nanomaterials, etc.

Using mainly data available for Guadeloupe, Martinique, Réunion Island and Mayotte, ANSES was able to carry out a risk assessment for around fifty of these chemicals in the following categories: UV filters, pesticides, hydrocarbons and metals. This report shows that half of the chemical substances assessed may pose risks to coral reefs and contribute to their degradation.

"To carry out this work, we relied on a study by the French Biodiversity Agency (OFB) and PatriNat (OFB-MNHN-CNRS-IRD), which lists chemicals likely to have toxic effects on corals. We then cross-referenced the danger thresholds applicable to corals for these substances with the concentration levels observed in the environment. This enabled us to identify the substances at risk for corals in Guadeloupe, Martinique, Mayotte and Réunion," explains Karen Burga, coordinator of these activities.

The number of substances potentially toxic to corals is very probably underestimated. In fact, given the lack of available data, work could only be carried out on a limited number of substances out of all those potentially found in coral reefs.

Reducing the release of chemicals into the marine environment

The Agency recommends creating or strengthening the monitoring and surveillance of chemicals that have an impact on coral reefs. Given the different distribution areas of coral reefs, it recommends that this monitoring be incorporated into the marine environment protection conventions applicable to the relevant marine areas (Cartagena Convention, etc.). 

"As we progressed with the collection of exposure data, we found significant differences in the levels of information available for each of the overseas territories studied (i.e. all the overseas territories except French Guyana, Saint Pierre and Miquelon). Most of the information came from the monitoring systems generated by the implementation of the EU Water Framework Directive. However, these monitoring systems do not exist for some territories, such as Wallis and Futuna and Saint-Barthélemy, which means that it is currently impossible to assess the risks of the chemicals in question," explains Karen Burga.

Furthermore, in order to protect coral, which is already under threat from the effects of climate disruption, ANSES is calling for the release of hazardous substances to be limited at the source through management measures, such as the application of restrictions on the use of chemicals or bans on their marketing under regulations like REACH.

Finally, it recommends improving both the choice of location and the operation of wastewater treatment systems.

Sunscreens: claims that must be justified

For the UV filter category, the report identified three substances in particular as toxic for corals: oxybenzone, octinoxate and octocrylene. A number of sunscreen products carry labels or pictograms highlighting their respect for the marine environment. These markings must be supported by studies carried out under the responsibility of the manufacturers selling them. The presence of one of the substances mentioned above seems incompatible with the possibility of benefiting from such claims.