The “lungs of the Mediterranean” under threat

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Tunisian marine biologist Yassine Ramzi Sghaier inspects seagrass beds: he says protecting the plant is crucial for a country already in the grip of a severe economic crisis.

Beneath the Mediterranean waters off Tunisia, gently undulating green seagrass beds provide vital marine habitats for fishing fleets and an erosion buffer for the beaches on which the tourism industry depends.

More importantly, seagrasses are such a key carbon store and oxygen producer to slow the devastating effects of climate change that the Mediterranean Wetlands Initiative (MedWet) calls them the “lungs” of the sea.

But, just as human actions elsewhere are devastating tree forests on earth, scientists warn that human activity is driving the grass under the sea to destruction at high speed, with disastrous environmental and economic impacts.

Named Posidonia oceanica after the Greek god of the sea Poseidon, seagrasses stretch across the Mediterranean seabed from Cyprus to Spain, absorbing carbon and reducing the acidity of the water.

“Posidonia oceanica…is one of the most important sources of oxygen supplied to coastal waters,” says MedWet, a 27-member regional intergovernmental network.

Tunisia, on the North African coast, “has the largest grasslands” of all, spanning 10,000 square kilometers (3,900 square miles), marine ecologist Rym Zakham-Sraieb said, highlighting its key role in carbon capture.

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.

A Tunisian fisherman enters the port of Ghar el-Melh;  fishing accounts for 13 percent of Tunisia's GDP, and nearly 40 percent of it is d

A Tunisian fisherman enters the port of Ghar el-Melh; fishing accounts for 13 percent of Tunisia’s GDP, and nearly 40 percent of it takes place around seagrass beds.

“We need Posidonia to capture as much carbon as possible,” Zakhama-Sraieb said.

But a dangerous cocktail of endemic pollution, illegal fishing using bottom trawl nets tearing up the seagrass and a failure of people to appreciate its vital importance is sounding the death knell.

“The Sea Has Been Destroyed”

Growing at depths of up to 50 meters (165 feet), the seagrass beds provide shelter for fish and slow coastal erosion by breaking up wave swells that would otherwise damage the sandy beaches that tourists love.

Tunisian marine biologist Yassine Ramzi Sghaier said the herb is crucial for a country already in the grip of a crushing economic crisis.

“Tunisia’s entire economic activity depends on Posidonia,” Sghaier said.

“It’s the biggest job provider,” he said, noting that at least 150,000 people are directly employed in fishing and tens of thousands in the tourism industry.

Growing at depths of up to 50 meters (165 feet), seagrass beds provide essential shelter for fish

Growing at depths of up to 50 meters (165 feet), seagrass beds provide essential shelter for fish.

The destruction was rapid and the replacement slow. The aquatic plant, also known as Neptune grass, grows less than five centimeters per year.

Seagrass areas have been reduced by more than half in the Gulf of Gabes, a large area on Tunisia’s eastern coast, Sghaier said, with a 2010 study blaming overfishing and pollution.

Once upon a time, Posidonia and a multitude of marine species thrived there, but since the 1970s phosphate factories have dumped chemicals into the sea, causing further damage to the ecosystem.

Seagrass beds serve as vital shelter for fish to breed, feed and shelter.

Fishing accounts for 13 percent of Tunisia’s GDP, and almost 40 percent of it takes place around seagrass beds – and fishermen describe plummeting stocks.

“The sea has been destroyed,” said Mazen Magdiche, who casts his nets from the port of Monastir. “Chemicals are being dumped everywhere.”

Tunisia

Map of Tunisia.

Magdiche calculates his catch is three times lower than it was 25 years ago, but said he has little alternative income.

“There are fewer and fewer fish,” he said.

“You are not looking for the interests of the sea, but to feed your children,” he added.

‘Disaster’

Nearly 70% of Tunisia’s population lives on 1,400 kilometers (nearly 900 miles) of coastline, and for many Posidonia is seen as mere rubbish.

When the seagrasses are washed up on the shore, they mix with the sand to form large shoals that protect the coastline from swells and waves, experts say.

But sometimes bulldozers are used to “clean up” beaches, contributing to accelerated coastal erosion, with 44% of beaches already at risk of being washed away.

“We are helping to make the beaches disappear by removing the shoals (of sea grass),” said Ahmed Ben Hmida, of the Tunisian Coastal Protection and Development Agency.

  • Marine ecologist Rym Zakham-Sraieb (left) highlights the critical carbon-binding role the sea plant has for the warming planet

    Marine ecologist Rym Zakham-Sraieb (left) points to the critical carbon sequestration role the sea plant plays for the warming planet.

  • Beaches are a key asset for tourism, which provided Tunisia with a record 14% of GDP in 2019 -- and seagrasses provide ak

    Beaches are a key asset for tourism, which provided Tunisia with a record 14% of GDP in 2019 – and seagrass beds provide them with a key erosion buffer.

Beaches are a key asset for tourism, which provided Tunisia with a record 14% of GDP in 2019 and supported up to two million people, or one-sixth of the population.

The aquatic plant also improves water quality, making beaches more attractive to tourists, Zakhama-Sraieb said.

Ben Hmida said creating four marine protected areas could help Posidonia, but this action was needed on a much larger scale.

“If nothing is done to protect all of the Tunisian posidonia, it will be a disaster,” he said.


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© 2022 AFP

Quote: ‘Lungs of the Mediterranean’ at risk (2022, May 2) retrieved May 2, 2022 from https://phys.org/news/2022-05-lungs-mediterranean.html

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