Red algae washes up on Brittany beaches as clean-up begins
Red algae can present a health risk when large quantities begin to decompose
The clean-up operation started on June 11
Martin Florent/Shutterstock and Saint-Gildas-de-Rhuys commune Facebook post
Large quantities of red algae have washed up on beaches in Brittany far earlier than usual this year, a phenomenon local officials say is linked to rising temperatures and warmer spring weather.
The commune of Saint-Gildas-de-Rhuys in Morbihan began its first clean-up operation of the season on June 11 to ensure beaches remain accessible to visitors.
"The first beach cleaning operation of the season will take place on Port Maria beach," the commune said in a Facebook post, noting that a prefectural order issued on July 18, 2024 authorises the removal of algae when large quantities wash ashore during the summer season.
Officials added that the equipment used for the operation is adapted to the natural environment and designed to minimise its impact on the wrack line.
The collected algae will be spread on agricultural land as fertiliser. According to local authorities, around 30 farmers in the area participate in the programme. The practice provides a sustainable way of managing the algae while enriching soil with organic matter. Last year, 554 hectares of farmland were amended using the collected seaweed.
Red algae and brown algae naturally develop on rocky reefs off the Rhuys Peninsula when temperatures and nutrient levels are favourable.
Depending on weather conditions, including storms, strong winds, swell and tides, large quantities can become detached and wash ashore.
However, these strandings are occurring increasingly early in the year, said Frédéric Pinel, mayor of Saint-Gildas-de-Rhuys, as reported by France 3.
While they traditionally took place around the height of summer, they are now often appearing in May and June as spring temperatures rise.
"Forty or fifty years ago, they tended to arrive around October," Mr Pinel said. "Now we see them in summer. Warming temperatures are accelerating the growth of the algae."
The clean-up programme is expected to cost the commune approximately €75,000. Part of that expense will be reimbursed by the Vannes urban community, while additional funding is provided by the Departmental Directorate of Territories and the Sea.
Last year, around 4,700m³ of algae were collected from the beaches of the Rhuys Peninsula.
Can red algae pose a health risk?
Like green algae, red algae can present a health risk when large accumulations begin to decompose during periods of hot weather.
As decomposing algae ferment, they can release hydrogen sulphide (H₂S), a toxic gas. For this reason, local authorities advise people against entering affected areas; walking on decomposing algae; disturbing the sand; or allowing pets access to sites where large accumulations are present.
According to the US Centers for Disease Control and Prevention (CDC), some harmful algal blooms can produce toxins that cause symptoms including stomach pain, skin irritation, headaches and respiratory problems. However, the principal concern identified by local authorities in Brittany is not algal toxins but hydrogen sulphide gas released when large quantities of stranded seaweed decompose.
Anyone who experiences symptoms after exposure should seek medical advice. Pet owners should contact a veterinarian immediately if an animal shows signs of illness after contact with algae, as poisoning can worsen rapidly. Symptoms in animals may include vomiting, lethargy, stumbling, loss of coordination and seizures.
