How heatwaves are threatening the Mediterranean

STORY: In the warm Mediterranean waters around Tunisia - fishermen here say they've been fighting off an invasion.

“Before “ISIS” appeared, we used to find fish, but now we no longer find anything.”

By "ISIS" - they mean these small blue crabs.

They're an invasive species that's exploded in these waters - as other sea life are dying off due to marine heatwaves.

And there's no end in sight to their takeover.

The crab earned its nickname due to its ferocity and destructive ability - devouring smaller fish around it.

As the Mediterranean continues to heat up - that's provided the perfect breeding ground for its larvae - which thrive in toasty temperatures.

Fisherman Salah Zawem says a decade ago, his nets were full of fish and octopus.

“It is a big problem. Look how long we have been pulling out the nets and what we found, just one, how much will this bring us? Nothing.”

But the invasion of these blue crabs point to a larger issue the area is facing.

Climate change is making the Mediterranean among the world's fastest warming seas – with temperatures rising about 20 percent faster than the global ocean average.

That's partly due to the fact that it's a relatively shallow and contained basin - which, experts say, makes it a climate change hotspot.

Hamdi Hached is an environmental engineer and climate specialist.

“The rise of temperatures in the Mediterranean sea is obvious. Last June, recorded sea water temperature was 11 degrees higher than usual. This means a drastic change in sea water temperature which will have an effect one way or another, as we know that temperature is the biological key to the reproduction of many types of organisms that live in the sea or even on land as well.”

According to research in the journal Climate Dynamics, the Mediterranean could suffer at least one long-lasting, severe heatwave every year between now and 2100.

And that could open the door to even more invasive species.

A 2021 report by the WWF says nearly 1,000 alien species have entered the sea - and about 10 percent of them today are considered invasive.

So - some are trying to find a way to adapt to this new reality - like Habib Zrida. He's the owner of a fishing company that now exports the blue crab.

And he's not alone. There are more than 30 factories processing the crabs, and the value of its exports doubled to $7.2 million from May 2020 to 2021.

Zrida says fishermen now want to work with the blue crab - and that they've gone from a curse - to a source of livelihood.