Invasive fish push west as Mediterranean sea slowly turns tropical | Marine life


PAsquale Tuccio moored his little blue and white wooden boat at the old pier in Linosa, one of Italy’s small Pelagic Islands in the Strait of Sicily. Inspecting his gillnet, he finds a sea cicada, sea bream, a bunch of parrotfish – and about six rabbitfish. Unlike his fishing companions, who reject rabbitfish, Tuccio will bring them home for his cat. The fish have poisonous spines, however, and he still remembers his first encounter with them. “I was only stung once,” said Tuccio. “I hope it doesn’t happen again. It was so painful.

Rabbit fish Siganus luridusalso known as dark spinefoot – is a tropical species, native to the Indian and Pacific Oceans. After the opening of the Suez Canal in 1869, the rabbitfish entered the eastern Mediterranean, making their way into Greek waters in 1964. They have since moved to the central Mediterranean, where they have found their food in abundance. favorite: seaweed. In recent years, rabbitfish have multiplied in the waters around Linosa, where they devour underwater vegetation. Researchers found it as far west as France.

A school of rabbitfish grazes on a reef in the waters around Greece. Photograph: Thanos Dailianis / Getty

Siganus luridus do not swim west alone. Among the more than 70 tropical fish that have made their home in the Mediterranean, lionfish (Pterois miles), silver-cheeked toadfish (Lagocephalus sceleratus), blue dotted cornet (Fistularia commersonii) and Golani herring (Etrumeus golanii) have been spotted in increasingly westerly waters. As the sea warms and becomes saltier due to human-induced global warming, tropical latitudes fish find more welcoming habitat in an area that, at least nominally, is temperate, not tropical.

“This is also happening in other parts of the world,” says Fiona Tomas Nash, marine ecologist at the Mediterranean Institute for Advanced Studies. “In Australia, Japan, South Africa, you see these tropical fish spreading to temperate zones – and it’s clearly linked to warming.”

While divers can welcome these tropical visitors to the Mediterranean, marine scientists are concerned about threats to biodiversity, public health and fisheries. A change from temperate to tropical would affect and affect the entire Mediterranean ecosystem. Rabbitfish, for example, eat so much that they turn kelp forests into sterile waste, destroying important growth habitats for native species.

Some fish arriving through the Suez Canal are even more harmful. In 2005, off the coast of southeast Greece, a fisherman spotted a solitary silver-cheeked toadfish (Lagocephalus sceleratus). A few years later he was all around the islands – from Crete to the Dodecanese and Cyclades. In 2017, a silver-cheeked toad was captured off Ceuta, near Gibraltar; others have been seen off Catalonia.

Mediterranean fisherman in boat
Mediterranean fishing is threatened by invasive tropical species.
Photograph: Yorgos Doukanaris / Pacific Press / Alamy

Poisonous to eat, they also tear up fishing nets to loot catches of squid, cuttlefish and other species of commercial value.

“We know very little about potential predators [of the silver-cheeked toadfish]even in native habitats, ”explains Paraskevi Karachle, an ichthyologist at the Hellenic Center for Marine Research in Greece who studies alien species. “In the Mediterranean, we have recorded a few, such as Caretta caretta and groupers, as well as recent observations of cannibalism.

In order to control their numbers, researchers are experimenting with possible uses of the silver-cheeked toadfish, such as fishmeal for the aquaculture industry, or the extraction of its toxin for cosmetics and pharmaceuticals. But the viability of these applications is uncertain.

“Until 20 years ago, tropical species were confined to the eastern parts of the Mediterranean,” explains Ernesto Azzurro of the Italian National Research Council, who, together with Manuela D’Amen at the Anton Dohrn zoological station, assessed the risk of species invasion. in the Mediterranean in the context of future climate scenarios. “Scientists at the time theorized the existence of a new biogeographic province, which on the western side did not extend beyond the Strait of Sicily.”

However, in the 21st century, the so-called Lessepsian invaders – as Indo-Pacific migrants are called, after Suez Canal developer Ferdinand de Lesseps – have categorically crossed this theoretical border. Between 1985 and 2006, the temperature of the Mediterranean rose by around 0.4 ° C each decade, adding pressure on already overexploited native species while favoring fish that thrive in warmer waters.

Linosa Island, Pelagie Islands, Sicily, Italy
The coast of Linosa. Invasive rabbitfish devoured the underwater vegetation. Photograph: Alamy

Future climate scenarios from the United Nations Intergovernmental Panel on Climate Change, applied to species distribution models, show how the western Mediterranean will become increasingly habitable for tropical fish, as will the southern Mediterranean. ‘Adriatic and the southwest coast of Italy. Newcomers can also change as they adapt. Some scientists argue that the lionfish – spotted off Puglia, Italy and Albania in 2019 and 2020 – could extend its temperature range, facing the colder winter waters of some Mediterranean areas, like this happened with the lionfish in the United States.

Humans also adapt. While in Linosa, rabbitfish is only suitable for the cat from Tuccio, Cyprus, where it has been around for some time, it is considered a delicacy and costs € 25 (£ 21) per kilo. Meanwhile, in Kastellorizo, in the Greek Dodecanese Islands, it’s peeled, fried, and served with a dash of vinegar. The idea is, if you can’t beat them, eat them.

A lionfish (Pterois miles)
A lionfish off the north coast of Lebanon. Some scientists claim that the fish are already adapting to cooler winters in parts of the Mediterranean. Photograph: Ibrahim Chalhoub / AFP / Getty

“The Mediterranean is suffering from tropicalization and this will continue,” says Nash. Efforts to create marine protected areas and restore ecosystems to make them more resilient to global warming and invasions can help, she says, but they are unlikely to reverse the trend, especially without full cooperation. between states. “Nature knows no borders, does it?

“Even in the best-case scenario, these invasions will continue,” says Azzurro, who also works with marine protected areas to involve communities in monitoring changes in biodiversity. “Ours will be an increasingly tropical sea.”

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