The fishermen of Mdiq, 13 km from Tetouan in northern Morocco, had never imagined that an invader could measure 10 cm and look like tea leaves, but "the sea is always full of surprises," says Abdellah Imrane resignedly, while cleaning his fishing nets of brown algae. For four years now, this seaweed has weighed down the nets, which end up sinking to the bottom of the water, preventing fish from clinging to them. "I've been fishing here for 35 years, swimming here. I had never seen it; it’s not from here.”
Originally from Japan, brown algae or Rugulopterix okamurae is an invasive species that grows very quickly. Youness Baghdidi, president of the Fnideq Champions Association for Scuba Diving and Environmental Protection, remembers having seen it for the first time in 2017 in a few places. "During my dives, I notice each time that the algae spreads very quickly and where it develops, the fish are rarer," he explains to us.
The speed of its development and its consequences are worrying the authorities, pushing the National Institute for Fisheries Research to begin underwater explorations in 2019. For the moment, there is still no precise mapping of the presence of the seaweed on the Moroccan coast but according to observations, the seaweed has invaded the natural habitat of certain species. “We have found that in the Jebha region, algae have taken the place of the habitats of sea anemones, for example,” says Mohammed Idrissi Malouli, director of INRH Tangier.
Fragile marine ecosystems are threatened by this invasive species that nothing seems to stop. Even its texture prevents fish from consuming it, ensuring it proliferates even faster. For Nadia Berdei, head of the fisheries and aquaculture department at the Agronomic and Veterinary Institute of Rabat, the expansion of brown algae is hastened by favorable reproduction conditions in the Mediterranean
"We have observed that the proliferation peak of Rugulopterix okamurae in 2015 coincided with a peak in sea surface temperature at Mediterranean level,” she says.
How could a seaweed from Japan make it to the Mediterranean? The most plausible theory, according to scientists, is that the brown algae, like many invasive species, traveled in ballast water, those reservoirs intended to stabilize ships. Abdelhak Naguib, a cargo captain, explains to us that “during the ballasting of a ship, large quantities of seawater are pumped and many marine species are involuntarily embarked inside the ship. The few specimens that survive during the trip will be thrown back into the sea in another port and therefore another ecosystem."
To prevent the proliferation of aquatic invasive species in ships' ballast water, the member countries of the International Maritime Organization adopted in 2004 the international convention for the control and management of ships' ballast water and sediments, commonly known as the BWM convention. The text came into effect in 2017 and its implementation is being done gradually by 2024.
“In one year, all ships must be equipped with a ballast water treatment system either by chemical or ultraviolet treatment. The goal is to eliminate invasive species that can live in these ballast waters,” says Abderazzak Atide, head of the maritime safety department at the merchant marine department.
According to scientists, nearly 1,000 invasive species have entered the Mediterranean over the past four decades. In addition to brown algae, the blue crab, native to the Caribbean, undermines fishing throughout the basin, including in Tunisia, France and Spain. This voracious species, which is growing at an exponential rate, arrived on the Moroccan Mediterranean coasts about four years ago and has even recently reached the Atlantic coasts as far as Essaouira. But if it is possible to regulate the development of the blue crab by putting it on people's plates, things are much more complicated with brown algae. Currently, the valorization of seaweed is the subject of research at several universities. A collaboration between Spanish, Portuguese, Italian and Chinese researchers focused on the pigments and antioxidants present in this species. The conclusions are very promising for medicine but also for the cosmetics and food industries.
While waiting for the projects to come out of the laboratories and in front of the huge piles of seaweed on the beaches of Martil not far from Tetouan, the women of the artisanal fishing cooperative Moquida are thinking about the use of brown seaweed in agriculture, as a fertilizer. Khadija Habyby, the president of the cooperative, is convinced: "Everything that comes out of the sea is good for the earth," she says.
Listen to Sofia Fagroud's report in French here:
This story was produced with support from Internews' Earth Journalism Network. It was first published in En Toutes Lettres and SNRT on 3 April 2023 in French; this version has been adapted by EJN's Mediterranean Media Initiative.
Banner image: Seabed with red algae, Morocco, 2023 / Credit: Association Abtal Fnideq.