KERKENNAH ISLANDS, Tunisia, November 13 (Reuters) – A decade ago, Tunisian fisherman Ahmed Chelli filled his nets with fish and squid he sold at the local market on the Kerkennah Islands. Today he only mentions “ISIS” – the name given by locals to the blue crabs that have invaded their fishing grounds in the rapidly warming waters of the Mediterranean.
“The fisherman… instead of finding fish to earn an income, he finds something to cut his nets,” Chelli complained.
For more than 70 days this summer, a marine heatwave has boiled the waters of the western Mediterranean.
It was the worst heat for the western part of the basin in four decades, said marine ecologist Joaquim Garrabou of Spain’s Institute of Marine Sciences, who monitors temperature gauges in the sea’s near-shore waters.
Temperatures were rising higher and the heatwave was lasting longer than any other to hit waters west of Sicily since records began in 1982, Garrabou said based on preliminary results of his analysis exclusively made available to Reuters.
“We have observed heat waves in the sea for the last 20 years,” said Garrabou, who is also the coordinator of the marine monitoring network T-MEDNet. He and his colleagues have found that about half of the worst heatwaves since 2015 have occurred across the basin.
“Almost every year, part of the Mediterranean suffers,” he said.
Measurements by European Space Agency satellites show that from June to September, water temperatures off North Africa and southwestern Europe were 2 to 5 degrees Celsius above the daily average for 1985-2005. Temperatures reached almost 31°C in some places.
Populations of sponges, starfish, fish and molluscs died en masse in the waters off France and Spain in September. Coral bleached to bone white.
In Tunisia, the underwater heat encouraged the reproduction of invasive species like the blue crab, said Hamdi Hached, an environmental adviser in Tunis at the Friedrich Naumann Foundation for Freedom.
The crabs likely first arrived from the Indo-Pacific via ship ballast water and were first documented in the Mediterranean in 1898. But with the last decade of warming, populations have exploded — eating and displacing valuable native species.
With blue crab larvae thriving in water temperatures around 30°C there is no end in sight.
Hached said the crustacean’s “savagery and destructive ability” inspired the caliphate-inspired moniker “ISIS” from fishermen of the Kerkennah Islands — which lie about 20 km (12 miles) off Tunisia’s north coast.
“It has a very large appetite to devour all creatures around it, becoming a bane for fishermen in the region.”
MILLIONS RELY ON THE SEA
While tourism drives most of the sea’s economic activity, which was worth US$450 billion in 2017 according to the World Wildlife Fund, there are millions who rely on the bounty of the sea for their livelihood.
But as climate change turns the Mediterranean Sea into one of the world’s fastest-warming seas — with temperatures rising about 20% faster than the global ocean average — this bounty is under threat.
The rapid warming is partly due to the fact that the Mediterranean Sea is a relatively shallow and confined basin. Covering an area of about 2.5 million square kilometers (970,000 square miles), it’s a “climate change hotspot because it’s a small sea,” Garrabou said.
There are few connections between the sea and the Atlantic to the west, so “there aren’t many pathways for warm water,” he said. Overall sea temperature today is on average 0.4°C higher than it was 30 years ago, data shows.
Acute marine heat waves can occur when warm air temperatures coincide with stable ocean conditions – when there is less mixing between the colder, deeper water layers and the warmer surface layer.
This summer, southern Europe suffered from sweltering temperatures on land, which scientists say provided the perfect conditions for an oceanic heatwave to spread through the waters as the ocean soaks up excess heat in the atmosphere.
The Mediterranean is not the only sea in hot water.
A 2016 marine heatwave along Chile’s southern coast caused huge algal blooms that wiped out fish farms and cost the aquaculture industry about $800 million, said scientist Kathryn Smith of the Marine Biological Association of the United Kingdom.
Another heatwave in Australia’s Tasman Sea lasted more than 250 days between 2015 and 2016, triggering outbreaks of disease on shellfish farms.
As the world warms, more frequent heat waves are expected to occur in the ocean, according to the United Nations Intergovernmental Panel on Climate Change. Climate change has already helped increase the annual number of ocean heatwave days by 54% between 1925 and 2016, a team of international scientists found in 2018.
Scientists say the Mediterranean could experience at least one prolonged, severe heatwave every year by 2100, according to a 2019 study in the journal Climate Dynamics.
Blue crabs aren’t the only animals making their way into the warmer Mediterranean Sea. Nearly 1,000 alien species have entered the sea, mostly by hitchhiking on ships, according to a 2021 report by WWF. But warmer temperatures have made it easier for some stowaways to establish populations.
Today, around 10% of these species are considered invasive, meaning they are likely to cause ecological or economic damage.
The bright yellow rabbitfish, for example, is overgrazing seagrass beds, destroying plants that provide important habitat for local species and sequester carbon.
Although economists have yet to fully consider the effects of ocean heat waves, recent experiences have many concerned.
In the waters off Greece, where the coastal zone accounts for about 69% of the national economy, a sea heatwave devastated the country’s mussel harvest last year, halving production and wiping out 80% of this year’s baby mussel seeds.
Fisheries in the Mediterranean are valued at over $3.4 billion, according to a 2022 IPCC report, with more than 76,000 fishing vessels scouring the azure waters for anchovies, bluefin tuna and red mullet in 2019.
The effects of such heatwaves are particularly severe in North Africa, where many “communities are engaged in small-scale fishing,” said Mauro Randone, who directs WWF’s Mediterranean programme, which focuses on the regional economy. “They are one of the most affected sectors.”
PLANNING FOR THE FUTURE
North African countries have started developing strategies to adapt to climate change, said Naguib Amin, who heads Clima-Med, an EU-funded climate protection group founded in 2018.
Speaking at the COP27 climate summit in Egypt, Amin told Reuters the group was working to develop climate change mitigation strategies for cities along the southern coast of the Mediterranean.
Europe’s coastal countries are facing similar effects from rising temperatures, but “the difference is in the financial capacity of these countries,” he said.
African nations hope COP27 will lead to more funding for projects that will help their communities adapt to warming oceans, he said.
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 fill a €6 billion investment gap in support of nations on the south coast of the Mediterranean to close sea .
But those efforts will take time to build momentum.
For now, Tunisia’s fishermen have had to find a solution to losing much of their traditionally caught species: fishing the blue crab commercially.
As of May 2021, blue crab exports from the country were valued at $7.2 million — more than double the same period in 2020, according to the Food and Agriculture Organization.
And there are now more than 30 factories processing crab – two of which are on the Kerkennah Islands.
“Fishermen now want to work with the blue crab,” said Habib Zrida, owner of a fishing company that now exports the crab. “It has become a source of livelihood after it was a curse.”
Reporting by Gloria Dickie in London and Sharm el-Sheikh, Egypt and by Jihed Abidellaoui on Kerkennah Island, Tunisia; Additional reporting by Karolina Tagaris in Athens, Catarina Demony in Lisbon and Kate Abnett in Brussels; Edited by Katy Daigle and Daniel Flynn
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