Science

In Tunisia, Posidonia seaweed is endangered – Science et Avenir

In Tunisia, Posidonia, a seagrass on which fishing and tourism depend, a vital sector of the country’s economy, is in danger of disappearing due to neglect, illegal fishing and pollution, scientists are alarmed.

“Tunisia has the largest seaweed beds in the Mediterranean, over a million hectares,” Rym Zahama-Sraieb, a Tunisian marine ecology researcher, told AFP.

These underwater forests, up to 50 meters deep, provide shelter for many species of fish. The leaves of “Posidonia oceanic” also contribute to the breaking of waves and thus to the preservation of the coast from erosion.

“The existence of all Tunisian economic activity depends on Posidonia, which is the largest provider of jobs in the country,” warns marine biologist Yassine Ramzi Sguier, referring in particular to the fishing sector (150,000 jobs) and tourism (tens of thousands) .

A bunch of leaves, roots and rhizomes – creeping stems usually buried in the ground – Posidonia grows very slowly, less than five centimeters per year.

Thanks to the rhizomes, grasslands store carbon and produce oxygen, which is why posidonia is called “blue carbon,” explains Ms Zahama-Sraieb, pointing out that it produces 14 to 20 liters of oxygen per square meter.

– “Maximum carbon” –

Seagrasses, which take up three times as much carbon as a forest, can fix large amounts of carbon for thousands of years, the researcher said.

“In the context of climate change, we need posidonia to capture as much carbon as possible,” agrees Yassine Ramsay Sguier, an expert in marine biology.

Due to a lack of resources, researchers cannot quantify the destruction of grasslands in Tunisia in recent years.

But they point to many causes in a country where almost 70% of the inhabitants live on 1,400 km of coastline: human activities, coastal development, illegal fishing, kelp aquaculture farms…

For example, due to the ignorance of the general public and decision makers, Posidonia “benches” washed up on the beach are often considered waste.

Bulldozers are sometimes used to evacuate them, removing a lot of sand and accelerating erosion, according to researchers who fear the disappearance of nearly half of Tunisian beaches.

Even stuck on the shore, the “benches” of Posidonia protect the shores from swell. They also improve water quality and transparency, making bathing more attractive for tourists,” recalls Dr. Rym.

In Tunisia, beaches are one of the main assets of tourism, a sector that accounts for up to 14% of GDP depending on the year. However, 44% of the country’s beaches are at risk of erosion due to rising sea levels.

“We are helping the disappearance of beaches by removing the benches,” warns Ahmed Ben Hmida, manager of maritime and coastal areas at the state agency for coast protection and development (Apal).

– “Destroyed Sea” –

According to scientists, almost 40% of fishing activity is in seaweed beds. A sector that accounts for 13% of Tunisia’s GDP.

A 2010 study noted a massive regression of seaweed beds in Gabes Bay (southeast) due to illegal fishing (seaweed trawling) and pollution.

Since the 1970s, phosphogypsum has been dumped there by chemical phosphate plants. The result: less than 40% of Posidonia meadows remain in this region, regrets Yasin Sgayer.

Even if he fishes further north, in Monastir (centre-east), Mazen Magdiche catches three times less fish than he did 25 years ago: “In the shallow waters where there is Posidonia, there are fewer and fewer of them.”

This man with weathered features has realized the importance of posidonia, but he understands his colleagues, in particular “small fishermen with ridiculous means”: “You do not seek the interests of the sea, but feed your children, your family.” .

Today, says the fisherman, “the sea is destroyed. Chemicals are being dumped everywhere. Our sea has changed.”

But Apal’s Ahmed Ben Hmida wants to “keep hope of saving this treasure”, in particular through “the forthcoming creation of four marine and coastal protected areas: Galite Islands (North), Zembra (Northeast), Kuriat (Northeast) and Kneis (east)”.

But he warns: “If nothing is done to protect all of Posidonia, we are heading for a real disaster.”

Back to top button