Mediterranean marine heatwaves threaten coastal livelihoods

Mediterranean marine heatwaves threaten coastal livelihoods

KERKENNAH ISLANDS, Tunisia, Nov 13 (Reuters) – A decade ago, Tunisian fisherman Ahmed Chelli’s nets were swollen with fish and octopus he sold at the local market in the Kerkennah Islands. Today he pulls nothing but “ISIS” – the name locals have given to the blue crabs that have invaded their fishing grounds in the rapidly warming waters of the Mediterranean.

“The fisherman, … instead of finding fish for income, he finds something that cuts his nets,” Chelli complained.

For more than 70 days this summer, a sea heat wave baked the waters of the western Mediterranean.

It was the worst sweltering for the western part of the basin in the past four decades, said marine ecologist Joaquim Garrabou of the Spanish Institute of Marine Sciences, which monitors temperature gauges in the sea’s coastal waters.

Temperatures have soared higher and the heat wave has lasted longer than any other to hit waters west of Sicily since records began in 1982, Garrabou said, based on preliminary results. of its analysis, shared exclusively with Reuters.

“We have witnessed marine heat waves over the past 20 years,” said Garrabou, who is also coordinator of the T-MEDNet marine monitoring network. He and his colleagues found that about half of the worst heat waves on record across the entire basin have hit since 2015.

“Almost every year, part of the Mediterranean suffers,” he said.

Measurements taken by European Space Agency satellites show that from June to September the waters off North Africa and south-west Europe were 2 to 5 degrees Celsius above daily averages from 1985-2005. Temperatures peaked at nearly 31C in some areas.

In September, populations of sponges, starfish, fish and molluscs were dying off en masse in the waters off France and Spain. Bone white bleached corals.

Around Tunisia, the underwater heat has encouraged the breeding of invasive species such as the blue crab, said Hamdi Hached, an environmental consultant in Tunis at the Friedrich Naumann Foundation for Freedom.

Crabs probably first arrived from the Indo-Pacific via ships’ ballast water and were first documented in the Mediterranean in 1898. But, with the last decade of warming, the population has exploded – eating and displacing valuable native species.

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

Hached said the pinched crustacean’s “ferocity and destructive capacity” inspired the caliphate-themed moniker “ISIS” to fishermen on the Kerkennah Islands – which lie about 20km (12 miles) off the northern coast from Tunisia.

“He has a very big appetite to devour all the creatures around him, becoming a curse to the fishermen in the area.”


While tourism drives most of the sea’s economic activity, worth $450 billion in 2017 according to the World Wide Fund for Nature, millions of people depend on the wealth of the sea for their livelihood.

But as climate change makes the Mediterranean one of the fastest warming seas in the world – with temperatures rising around 20% faster than the global ocean average – this wealth is under threat.

The rapid warming is partly due to the fact that the Mediterranean is a relatively shallow and confined basin. With 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 Ocean to the west, so there are “not many exit routes for warm water”, he said. Global water temperature is now 0.4C warmer on average than it was 30 years ago, the data shows.

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

This summer, southern Europe experienced scorching temperatures on land, which scientists say provided the perfect setup for an ocean heat wave to play out in the waters, as the ocean soaks up the excess heat in the atmosphere.


The Mediterranean is not the only warm water sea.

A 2016 marine heatwave along Chile’s southern coast caused massive algal blooms that wiped out fish farms and cost the aquaculture industry some $800 million, said scientist Kathryn Smith of the Marine Biological Association of the United Kingdom.

Another heat wave in the Tasman Sea in Australia lasted more than 250 days between 2015 and 2016, triggering outbreaks at shellfish farms.

As the world warms, marine heat waves are expected to become more frequent, according to the United Nations Intergovernmental Panel on Climate Change. Already, climate change contributed to a 54% increase in the annual number of ocean heat days between 1925 and 2016, a team of international scientists found in 2018.

Scientists say the Mediterranean could experience at least one severe, long-lasting heat wave every year by 2100, according to a 2019 study in the journal Climate Dynamics.


Blue crabs aren’t the only animals to invade the warmer Mediterranean. Nearly 1,000 alien species have entered the sea, according to a 2021 report by WWF, mostly by hitchhiking on ships. But warmer temperatures have made it easier for some stowaways to establish populations.

Today, about 10% of these species are considered invasive, meaning they are likely to cause environmental or economic harm.

Bright yellow rabbitfish, for example, overgraze seagrass beds, destroying plants that provide key habitat for local species and sequester carbon.

Although economists have yet to fully consider the impacts of marine heat waves, recent experience has many concerned.

In waters off Greece, where the coastal zone accounts for around 69% of the national economy, a sea heatwave last year ravaged the country’s mussel harvest, halving production and wiping out 80% young shoots of mussels for this year.

Mediterranean fisheries are valued at over $3.4 billion, according to a 2022 IPCC report, with over 76,000 fishing vessels trawling cerulean waters for anchovy, bluefin tuna and red mullet in 2019 .

The impact of such heat waves is particularly pronounced in North Africa where many “communities are involved in artisanal fishing”, said Mauro Randone, who manages WWF’s Mediterranean program focusing on the regional economy. “This is one of the hardest hit sectors.”


North African countries have started developing climate change adaptation strategies, said Naguib Amin, who leads Clima-Med, an EU-funded climate action group launched in 2018.

Speaking at the COP27 climate summit in Egypt, Amin told Reuters the group was working to develop climate action strategies for cities on the southern Mediterranean coast.

European coastal countries face similar impacts from rising temperatures, but “the difference lies 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 seas, 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 expenditure over eight years to help fill an investment gap of 6 billion euros to support the nations of the southern coast of the sea.

But this effort will take time to gain momentum.

For now, Tunisian fishermen have had to find a solution to the loss of a large part of their traditionally fished species: commercial blue crab fishing.

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

And there are now more than 30 crab processing plants, including two located in the Kerkennah Islands.

“Fishermen now want to work with the blue crab,” said Habib Zrida, owner of a fishing company that now exports the crabs. “It has become a source of income, after having been a curse.”

Reporting by Gloria Dickie in London and Sharm el-Sheikh, Egypt, and Jihed Abidellaoui on the island of Kerkennah, Tunisia; Additional reporting by Karolina Tagaris in Athens, Catarina Demony in Lisbon and Kate Abnett in Brussels; Editing by Katy Daigle and Daniel Flynn

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