• The cystoseires are found on the surface for certain species and up to 60 m deep for others.

  • These brown algae endemic to the Mediterranean are threatened by pollution, habitat destruction and overfishing by herbivore predators.

  • The team of scientists working in the Ecoseas laboratory at UCA re-establishes these plants in their natural environment after having grown them in the laboratory.

"It's like a forest of oaks but underwater, one of the most complex and fragile Mediterranean ecosystems", this is how Luisa Passeron Mangialajo, researcher at the University of Côte d'Azur (UCA) in the Ecoseas laboratory, illustrates the role of cystoseires, endemic brown algae found only in the Mediterranean and threatened with extinction.

“There are canopies, undergrowth, it serves as a refuge, a nursery and provides food for other species.

Cystoseira forests have a key role in the productivity of ecosystems and in the maintenance of biodiversity.

If they were to disappear, it would have the same consequences as if a forest on Earth disappeared.

It is for all these reasons that this researcher, who has been working on marine ecology since 2007, is trying to preserve these species with her team at the Ecoseas laboratory.

Overfishing by predators of sea urchins, one of the causes of the disappearance of cystoseires

“Some species of cystoseires are found on the surface, others up to 60 m in depth, develops the scientist.

In a few decades, we have lost a lot, especially in urban areas because they are very sensitive to pollution.

They also suffer the destruction of their habitat with the construction of ports or piers but also physical disturbances [trampling, boat anchors].

Their greatest threat is the proliferation of herbivores such as sea urchins, in particular because of the overfishing of their predators.

»

This is called a “trophic cascade”.

Luisa Passeron Mangialajo explains: “By intensively fishing sea urchin predators [sea urchins, sea bream, etc.], the latter multiply and graze on the algae, creating veritable underwater deserts, which are called

barren grounds

.

»

Reintroduce species

The Ecoseas laboratory then took matters into its own hands through the European Afrimed project for ecological restoration in marine forests.

In partnership with seven other countries, they have identified priority sites for action.

On the Côte d'Azur, this pilot project is being tested in Natura 2000 sites, in places where cystoseires are still present but also where they have disappeared.

“We have data which proves to us that there were algae in certain places in the 1970s. What we control less are the causes of their disappearance.

»

Luisa Passeron Mangialajo's team then collects “seeds” when the seaweed reproduces, studies them, cultivates them in the laboratory and then re-establishes them in their natural environment.

"We place supports, on which there are small shoots and we protect them, as much as possible, from herbivores", specifies the professor.

Two experiments are in progress and will be monitored throughout the summer.

To be sure that they work, "you have to wait at least a year to see if they are able, in turn, to reproduce"

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