Mediterranean marine heatwaves threaten coastal livelihoods
KERKENNAH ISLANDS, Tunisia: A decade ago, Tunisian fisherman Ahmed Chelli’s nets bulged with fish and octopus that he sold at the local market in the Kerkennah islands. Today, he pulls up only “ISIS” — the name locals have given to the blue crabs that have invaded their fishing grounds in the fast-warming waters of the Mediterranean.
“The fisherman, … instead of finding fish to provide an income, he finds something that cuts his nets,” Chelli complained.
For more than 70 days this summer, a marine heatwave cooked the waters of the western Mediterranean.
It was the worst swelter for the western part of the basin in the last four decades, said marine ecologist Joaquim Garrabou at Spain’s Institute of Marine Sciences, who monitors temperature gauges in the sea’s near-coastal waters.
Temperatures climbed higher, and the heatwave lasted longer, than any other to hit the waters west of Sicily since record-keeping began in 1982, Garrabou said, based on preliminary findings from his analysis, shared exclusively with Reuters.
“We’ve been witnessing marine heatwaves during the last 20 years,” said Garrabou, who’s also coordinator of the T-MEDNet marine monitoring network. He and his colleagues have found that about half of the worst heatwaves on record in the entire basin have hit since 2015.
“Almost every year, some area of the Mediterranean suffers,” he said.
Measurements taken by European Space Agency satellites show that, from June through September, the waters off north Africa and southwest Europe were 2 to 5 degrees Celsius above the 1985-2005 daily averages. Temperatures peaked at nearly 31C in some parts.
By September, populations of sponges, sea-stars, fish, and mollusks were dying en masse in the waters off France and Spain. Corals bleached to bone white.
Around Tunisia, the underwater warmth encouraged reproduction among invasive species such as the blue crab, said Hamdi Hached, an environmental consultant in Tunis at the Friedrich Naumann Foundation for Freedom.
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