Harmful algal blooms : when global warming puts the health of watersports users and bathers into risk


A new phenomenon on the Aquitaine coastline

Usually living in tropical warm waters, Ostreopsis siamensis is a microscopic single-celled seaweed which is invisible to the naked eye. Most of the time, it appears in coastal areas, and grows around macroalgae and rocks. When all the conditions are gathered, those seaweeds multiply and can cover a large surface. This phenomenon is called a blooming phenomena or efflorescence.

It is the first time that a bloom of Ostreopsis siamensis, as huge as this one, has been observed on the Atlantic coast. Some observations have been made, especially at the end of last summer on the Hendaye coastline, however none of them was of that scope. Global warming, which has lead to a higher global ocean surface temperature, has increased the number of areas that favour the development of this algae. Moreover, human activities such as maritime transport (via ballast waters), can also spread invasive species into new territories and waters.

The Ostreopsis siamensis bloom has risen major issues

A health risk

Flu symptoms, breathing difficulties, skin irritations, metal taste constitute the symptoms that can be observed after being exposed to toxins produced by this seaweed. This issue therefore needs to be taken seriously, as there can be severe consequences on human health. This explains why some preventive closings of most of the beaches occurred along the Basque coastline, from Biarritz to Saint Jean de Luz.   

A socioeconomic issue

Bathing and touristic activities are the first ones to be impacted by Ostreopsis siamensis, as beaches can close for a few days. If this type of efflorescence happens regularly, it will have an important impact on coastal economic activities during summertime. Now that Ostreopsis can be found around this coast, it can grow up again, when adequate living conditions are gathered. Hence, it is essential to anticipate new decision-making and monitoring processes, in case this type of algae blooms happens again in the future. 

Surfrider Foundation Europe's advocacy for bathing and recreational water quality in Europe

Surfrider Foundation Europe's Manifesto for bathing and recreational water quality in Europe advocates for the inclusion of new monitoring parameters within beach water quality testings, such as : marine litter, chemical pollutants, as well as Cyanobacteria and HAB (Harmful Algae Blooms), which relates to Ostreopsis siamensis and Ostreopsis ovata. The recent news have highlighted the importance of undertaking analyses for users’ health on a regular basis, and of reinforcing the current water quality monitoring program, in order to anticipate and avoid « crises » …

Nowadays, only the bacteriological parameter is taken into account within beach water quality testings. In addition to advocate for a broader number of parameters, Surfrider Foundation Europe campaigns to extend targeted coastal areas to watersport activities areas, to process to testing programs during the whole year and finally, to provide transparent available information for the public.

To learn more on bathing and recreational water quality in Europe : 2020 European bathing water quality Report : Surfrider Europe reacts and expresses its demands, June 3rd, 2021.

During the month of September, the European Union will launch its citizens participation for the review of the European bathing water quality Directive. We are counting on you to be part of this citizen participation, in order to help us pressuring European legislators, and thus adopting an ambitious review of the European Directive, which includes all the different parameters that can impact our health.

Click here to learn more about the algae Otreopsis ovata.

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