Tiny and insidious, microalgae are multiplying along our coastlines. Although vital to our survival, some 200 out of 5,000 species studied are harmful to people and ecosystems. As global warming intensifies the problem, our oceans may be growing ever more toxic. The Down to Earth team investigates.
Microalgae tend to be invisible to the naked eye, although occasionally algal blooms can be seen from space as they leave behind a trail of green, orange, brown, or even red sludge. It's a natural phenomenon, says Yoan Le Merrer, a marine scientist at French Institute for Ocean Science (IFREMER), but it's not entirely harmless.
Toxins released by toxic microalgae can lodge themselves into the livers of shellfish and cause serious illness to the unsuspecting consumer. Le Merrer and a team of scientists monitor the marine environment, scanning the ocean for toxic algae. If found in coastal areas, the institute can take a series of measures, including the removal of shellfish from supermarket shelves.
An abnormal proliferation?
Even though they pose a serious threat, microalgae are also vital to our survival. The micro-organisms absorb CO2 and produce half of the oxygen we breathe, as well as being a pillar in the food chain. It's the abundance of microalgae that is knocking ecosystems out of balance. When the algae decompose, oxygen is sucked out of the water, suffocating other marine creatures.
Researcher Philipp Hess studies the environmental conditions that favour the growth of toxic microalgae. "We have observed that microalgae originally from tropical parts of the world are also spreading in latitudes further north," he says, adding that algal blooms could spread as extreme weather events such as storms or heatwaves become more common.
Ocean detox
Thierry Larnicol, an oyster farmer in Brittany, has been forced to halt production several times, his shellfish exceeding the toxicity levels. Larnicol has now invested in a filtration system to remove toxins from the water and prevent contamination. It works by injecting bubbles into water columns, capturing the microalgae, and releasing the water back into the sea. "It's a huge investment," he acknowledges. With a price tag of at least €800,000, it's a sum that few farms can afford to pay.
Limiting chemical run-off from farms, mostly nitrates and phosphorus, is another solution. Found in fertilisers, the substances infiltrate the soil in farms, and eventually rivers and the ocean. Agronomist Anne-Monique Bodilis investigates the impact of farming practices on water quality.
Bodilis has a simple proposition: covering the soil with plants that can absorb nutrients. This can either be crops or a temporary plant that doesn't get harvested, but acts as a nitrate pump.
