In Tunisia, Posidonia, a prairie on which fishing and tourism depend, a crucial sector for the country’s economy, is in danger of disappearing, threatened by ignorance of its role, illegal fishing and pollution, scientists are alarmed .
“Tunisia has by far the largest seagrass beds in the Mediterranean”, more than one million hectares, assures AFP Rym Zakhama-Sraieb, researcher in marine ecology in Tunis.
These underwater forests, present up to 50 meters deep, offer shelter to many species of fish. The leaves of “Posidonia oceanica” also help to break the waves and therefore to preserve the coast from erosion.
“The existence of all Tunisian economic activities depends on Posidonia, which is the largest supplier of jobs in the country”, warns marine biology expert Yassine Ramzi Sghaier, citing in particular the fishing sectors (150 thousand jobs direct work) and tourism (tens of thousands).
A bundle 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, lawns store carbon and produce oxygen, which is why Posidonia is called “blue coal,” explains Ms. Zakhama-Sraieb, noting that it produces 14 to 20 liters of oxygen per square meter.
– “A maximum of carbon” –
According to the researcher, marine phanerogams, which absorb three times more carbon than a forest, can fix large amounts over thousands of years.
“In a context of climate change, we need posidonia to capture as much carbon as possible,” agrees marine biology expert Yassine Ramzi Sghaier.
Due to a lack of resources, researchers cannot quantify the destruction of meadows in recent years in Tunisia.
But they indicate multiple reasons in a country where almost 70% of the inhabitants live on 1,400 km of coastline: human activities, coastal development, illegal fishing, aquaculture farms set up on seagrasses …
Due to the ignorance of the general public and decision makers, the Posidonia “benches” brought ashore on the beaches are, for example, often considered waste.
Bulldozers are sometimes used to evacuate them, removing a lot of sand and accelerating erosion, according to researchers who say they fear the disappearance of nearly half of Tunisian beaches.
Even stranded on the beach, the “benches” of Posidonia protect the coasts from storm surges. They also improve the quality of the water and its transparency, making swimming more attractive to tourists, Dr. Rym recalls.
In Tunisia, beaches are one of the great resources of tourism, a sector that represents 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 to make the beaches disappear by removing the benches,” warns Ahmed Ben Hmida, head of marine and coastal areas with the government agency for the protection and development of the coast (Apal).
– “Sea destroyed” –
Almost 40% of the fishing activity also takes place in seagrass beds, according to the scientists. A sector that represents 13% of the GDP in Tunisia.
A 2010 study found a massive regression of seagrass beds in the Gulf of Gabes (southeast) due to illegal fishing (bottom trawling on seagrass beds) and pollution.
Since the 1970s, chemical phosphate treatment plants have dumped phosphogypsum there. Result: less than 40% of Posidonia meadows remain in this region, regrets Yassine Sghaier.
Although he fishes further north, in Monastir (center-east), Mazen Magdiche catches three times fewer fish than 25 years ago: “In the shallows where there is posidonia, there are fewer and fewer of them”.
This man with features marked by the elements has realized the importance of posidonia but he understands his colleagues, in particular “small fishermen with derided means”: “Do not seek the interests of the sea but to feed your children, your family “.
Today, says the fisherman, “the sea is destroyed. Chemicals are dumped everywhere. Our sea has changed.”
But Ahmed Ben Hmida of Apal wants to “keep the hope of saving this treasure”, in particular through “the imminent creation of four marine and coastal protected areas: the islands of Galite (north), Zembra (northeast), Kuriat ( northeast) and Kneiss (east) “.
But he warns: “If nothing is done to protect all the posidonia, we are headed for a real disaster”.