‘Lungs of Mediterranean’ at risk as seagrass dies off
Monastir – Under the Mediterranean waters off Tunisia, gently waving green seagrass meadows provide vital marine habitats for the fishing fleets and an erosion buffer for the beaches the tourism industry depends on.
Even more importantly, seagrass is such a key store of carbon and producer of oxygen – critical to slowing the devastating impacts of climate change – that the Mediterranean Wetlands Initiative (MedWet) calls it “the lungs” of the sea.
But, just as human actions elsewhere are devastating forests of trees on land, scientists warn that human activity is driving the grass under the sea to destruction at speed, with dire environmental and economic impacts.
Named Posidonia oceanica after the Greek god of the sea Poseidon, seagrass spans the Mediterranean seabed from Cyprus to Spain, sucking in carbon and curbing water acidity.
“Posidonia oceanica... is one of the most important sources of oxygen provided to coastal waters,” MedWet, a 27-member regional intergovernmental network, says.
Tunisia, on the North African coastline, “has the largest meadows” of all spreading over 10 000km2, marine ecologist Rym Zakhama-Sraieb said, pointing to its key carbon-capture role.
The underwater flowering plants absorb three times more blue carbon – the term used to describe the removal of carbon dioxide from the atmosphere by the ocean and coastal ecosystems – than a forest, and they can store it for thousands of years, she said.
“We need Posidonia to capture a maximum of carbon,” Zakhama-Sraieb said.
But a dangerous cocktail of rampant pollution, illegal fishing using bottom trawling nets that rip up the seagrass, and a failure by people to appreciate its life-giving importance is spelling its demise.
Growing at a depth of up to 50m, seagrass provides shelter for fish and slows the erosion of coastlines by breaking wave swells that would otherwise damage the sandy beaches that tourists like.
Tunisian marine biologist Yassine Ramzi Sghaier said the grass was crucial for a country already gripped by a grinding economic crisis. “All of Tunisia’s economic activity depends on Posidonia,” Sghaier said. “It is the largest provider of jobs,” he claimed, noting that at least 150 000 people are directly employed in fishing and tens of thousands in the tourism industry.
Destruction has been swift, and replacement slow. The aquatic plant, also known as Neptune grass, grows less than five centimetres a year.
Areas of seagrass meadows have been slashed by more than half in the Gulf of Gabes, a vast area on Tunisia’s eastern coast, Sghaier said, with a 2010 study blaming excessive fishing and pollution.
Once Posidonia and a wealth of marine species thrived there, but since the ’70s, phosphate factories have poured chemicals into the sea, causing more damage to the ecosystem.
Fishing makes up 13% of Tunisia’s GDP, and nearly 40% of it is done around seagrass meadows and fisherman describe plummeting stocks.
When seagrass is washed up onshore, it mixes with sand to form large banks that protect the coastline. But sometimes bulldozers “clean” the beaches, contributing to the acceleration of coastal erosion, with 44% of beaches at risk of being washed away.