Marine heat waves in the Mediterranean threaten coastal livelihoods

KIRKANAH ISLANDS, Tunisia, NOV 13 (Reuters) – (This story was corrected on November 13 to show that the sea temperature is 1.2°C higher than it was 30 years ago, not 0.4°C, in paragraph 18)

A decade ago, the nets of Tunisian fisherman Ahmed Cheli were bloated with fish and octopus that he sold at the local market in the Kerkennah Islands. Today, he’s only pulling “ISIS” – the locals’ name for the blue crabs that invaded their fishing grounds in the rapidly warming waters of the Mediterranean.

Shelley complained: “The fisherman… instead of finding fish for income, finds something to break his net.”

For more than 70 days this summer, a marine heat wave has cooked the waters of the western Mediterranean.

Marine ecologist Joaquim Garabo of the Spanish Institute of Marine Sciences, which monitors temperature gauges in waters near the coast, said the weather had been the worst in the western part of the basin in the past four decades.

Based on preliminary results from his analysis, Garabo said temperatures rose more, and the heatwave lasted longer than any other wave that hit waters west of Sicily since record-keeping began in 1982.

“We’ve had marine heatwaves for the past 20 years,” said Garbo, who is also the coordinator of the marine monitoring network T-MEDNet. He and his colleagues have have found About half of the worst heat waves on record have hit the entire basin since 2015.

“Almost every year, some areas of the Mediterranean suffer,” he said.

Measurements from European Space Agency satellites show that from June to September the waters off North Africa and southwestern Europe were two to five degrees Celsius above daily averages for 1985-2005. Temperatures peaked at nearly 31°C in some parts.

By September, groups of sponges, sea stars, fish and mollusks were dying en masse in the waters off France and Spain. Coral bleaching to become bone white.

Across Tunisia, underwater warmth has encouraged breeding among invasive species such as the blue crab, said Hamdi Hached, an environmental consultant in Tunisia at the Friedrich Naumann Foundation for Freedom.

Crabs likely first arrived from the Indo-Pacific by way of ships’ ballast water, and were first documented in the Mediterranean in 1898. But as temperatures have risen in the last decade, the population has spread – and eaten and outnumbered the species. local value.

With blue crab larvae thriving in water temperatures around 30°C, there is no end in sight.

Hached said that the “ferociousness and destructive power” of these crustaceans inspired the title of caliphate by the fishermen of the Kerkennah Islands, which lie about 20 kilometers off the northern coast of Tunisia.

“She has a very big appetite to eat all the creatures around her, becoming a curse on the fishermen in the area.”

Millions depend on the sea

While tourism drives most of the sea’s economic activity, worth $450 billion in 2017 according to the World Wildlife Fund, there are millions who depend on the bounty of the sea for their livelihoods.

But as climate change makes the Mediterranean among the world’s fastest-rising seas — temperatures rise 20% faster than the global ocean average — that bonus is at stake.

The reason for the rapid warming is partly due to the fact that the Mediterranean is a relatively shallow and impounded basin. With an area of ​​about 2.5 million square kilometers (970,000 square miles), it is a “climate change hotspot because it is a small sea,” Garabo said.

The links between the sea and the Atlantic Ocean to the west are few, he said, so “there aren’t a lot of ways to get warm waters.” The data shows that the overall water temperature is now 1.2°C higher on average than it was 30 years ago.

Sharp marine heat waves can form when warm air temperatures coincide with stable ocean conditions—when there is less mixing between cooler, deeper layers of water and a warmer surface layer.

This summer, southern Europe experienced extreme temperatures on land, which scientists said provides the perfect setting for an ocean heat wave to unfold in the waters, as the ocean absorbs excess heat into the atmosphere.

Economic costs

The Mediterranean is not the only sea in hot water.

The 2016 marine heat wave along the southern coast of Chile caused massive algal blooms that wiped out fish farms and cost the aquaculture industry about $800 million, said scientist Catherine Smith of the Marine Biological Society of the United Kingdom.

Another heat wave in the Australian Tasman Sea lasted for more than 250 days between 2015 and 2016, leading to outbreaks of disease in oyster farms.

As the world warms, marine heat waves are expected to become more frequent, according to the United Nations’ Intergovernmental Panel on Climate Change. Climate change has already helped increase the annual number of ocean heatwave days top 54% From 1925 to 2016, a team of international scientists found in 2018.

Scientists say the Mediterranean could experience at least one long-lasting severe heat wave every year between now and 2100, according to 2019. Research in Climate Dynamics magazine.

Invasive species

Blue crabs aren’t the only animals to invade the warmer Mediterranean. Nearly 1,000 alien species have entered the sea, according to 2021 Report By WWF, often by ship boarding. But warmer temperatures have made it easier for some stowaways to form populations.

Today, about 10% of these species are considered invasive, which means they have the potential to cause environmental or economic harm.

light yellow rabbitFor example, the overgrazing of seagrass beds, which leads to the destruction of plants that provide a key habitat for native species and sequestration of carbon.

Although economists have not fully taken into account the effects of marine heat waves, recent experiences worry many.

In the waters off Greece, where the coastal area accounts for about 69% of the national economy, last year’s marine heat wave destroyed the country’s mussel crop, halving production and erasing 80% of this year’s mussel seed.

Fisheries in the Mediterranean are valued at more than $3.4 billion, the Intergovernmental Panel on Climate Change for 2022 Report He said, with more than 76,000 fishing vessels trawling through the ceramic waters in search of anchovies, bluefin tuna, and red mullet in 2019.

The impact of such heat waves is particularly severe in North Africa where “many communities are involved in small-scale fisheries,” said Mauro Randoni, who directs the WWF’s Mediterranean Programme, which focuses on the regional economy. “It is one of the sectors most affected.”

Planning for the future

Najib Amin, Chairman of the Board, said North African countries are beginning to develop strategies for how to adapt to climate change Clima MedThe European Union funded Climate Action Group launched in 2018.

Speaking at the COP27 Climate Summit in Egypt, Amin told Reuters that the group is developing climate action strategies for cities on the southern coast of the Mediterranean.

He said coastal countries in Europe face similar impacts from rising temperatures, but “the difference is the financial capacity of these countries.”

He said African countries hope COP27 will lead to more funding for projects that will help their communities adapt to rising seas.

On Tuesday at COP27, European banks announced a partnership with the Union for the Mediterranean, which includes 42 countries, to provide grants and capital spending over eight years to help close a €6 billion investment gap to support countries on the southern coast of the sea. .

But that effort will take time to build momentum.

For now, Tunisian fishermen have to find a solution to the loss of many of their traditionally harvested species: commercial blue crab fishing.

In May 2021, blue crab exports from the country were valued at $7.2 million — more than double the value of the same time period in 2020, according to the Food and Agriculture Organization.

There are now more than 30 cancer treatment plants – two of them are located in the Kerkennah Islands.

“The fishermen now want to work with the blue crab,” said Habib Zuraida, owner of a fishing company that now exports crabs. “It became a source of livelihood after it was a curse.”

Additional reporting by Gloria Dickey in London and Sharm el-Sheikh in Egypt, and Jihad Obeidlawi in Kerkennah Island, Tunisia. Additional reporting by Carolina Tajares in Athens, Katrina Damon in Lisbon, Kate Abnett in Brussels; Editing by Katie Daigle and Daniel Flynn

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