{"id":16556,"date":"2024-10-29T15:39:13","date_gmt":"2024-10-29T14:39:13","guid":{"rendered":"https:\/\/www.mio.osupytheas.fr\/?p=16556"},"modified":"2024-11-02T15:58:50","modified_gmt":"2024-11-02T14:58:50","slug":"comment-lutter-contre-les-proliferations-dalgues-vertes-et-de-sargasses","status":"publish","type":"post","link":"https:\/\/www.mio.osupytheas.fr\/en\/how-to-combat-the-proliferation-of-green-algae-and-sargassum\/","title":{"rendered":"How can we combat the proliferation of green algae and sargassum?"},"content":{"rendered":"

In an article in The Conversation<\/a>, Philippe Potin, <\/span><\/a>CNRS Research Director (Roscoff Biological Station, Sorbonne University), provides an update on the proliferation of green algae on the Breton coast, which has an abundance of nitrogen in common with sargassum, which proliferates in the Caribbean. Research carried out at the MIO has clarified the role of diazotrophs, nitrogen-fixing bacteria, in the proliferation of sargassum.<\/p>\r\n \r\n

Read the article<\/strong><\/a><\/h4>\r\n \r\n

What do strandings of green algae in Brittany and sargassum in the Caribbean have in common? An abundance of nitrogen, which the algae can take advantage of through different mechanisms. While it is difficult to prevent the proliferation of sargassum, we can act at source to starve the green algae.<\/strong><\/p>\r\n

A recurring and all-too-predictable occurrence every summer, strandings of brown seaweed (sargassum) have once again been reported. in the Caribbean islands<\/a> in 2024. 6,000 km away, the Breton bays<\/a> were once again covered in their thick coat of green algae.<\/p>\r\n

In these areas, the nauseating smell of hydrogen sulphide emanating from the decomposition of these algae has become unbearable, and has even led to closing off access to beaches that were once paradise<\/a>. The accumulation of decomposing algae will also deplete the environment of oxygen, leading to a decline in biodiversity and even episodes of mass mortality in ecosystems.<\/p>\r\n

However, recent research has revealed that the origin of these proliferations is paradoxically different between temperate waters, which are saturated with nitrates, and tropical waters, which are very poor in nutrients and rich in organisms that fix atmospheric nitrogen.<\/p>\r\n\r\n

Well-established mechanisms<\/h4>\r\n

The mechanisms that trigger Breton green tides have been well established for over twenty years, thanks to the work of all the teams involved. by Ifremer in the 1990s<\/a>.<\/p>\r\n

These algae benefit from the presence of excess nitrates in coastal waters. Opportunistic, they are able to grow much faster than other species of algae as soon as light and current conditions are right.<\/p>\r\n

This is because watercourses, even those with modest flows, carry nitrogen from leakage caused by over-fertilisation of the land with mineral fertilisers and animal waste. Anaerobic bacteria (which can develop in the absence of oxygen) then carry on the process of fertilisation. degradation of organic matter<\/a>which generates gaseous fumes with a rotten egg smell, in particular hydrogen sulphide, an lethal gas in high doses<\/a> for humans and land animals.<\/p>\r\n

In the tropical Atlantic, paradoxically, bacteria play a vital role in the proliferation of sargassum brown algae<\/a>. As you move further from the coast, the ocean becomes depleted of dissolved nitrogen. To thrive, brown algae need to take advantage of all the resources available, whether they come from animals (fish, crustaceans, etc.) or from the sea, hydraires<\/a>) but also micro-organisms capable of fixing nitrogen from the air, which are found in these drifting ecosystems.<\/p>\r\n

From very recent results<\/a> indicate that these microbial symbioses are essential for maintaining the growth of Sargassum offshore, and that they contribute much more than large rivers to supplying Sargassum blooms with nitrogen.<\/p>\r\n\r\n

Without nitrogen, algae growth remains limited<\/h4>\r\n

Understanding the conditions under which algae proliferate is crucial, as it enables us to develop strategies to limit the environmental and health impacts and to better manage accumulations of algae on beaches.<\/p>\r\n\r\n