The coast of Italy is occupied by an exotic blue crab, a threat to ecosystems: how to recognize it

In recent years, the population of the blue king crab, an exotic species from the Atlantic, has literally exploded in France. What are the risks?

As the Superior Institute for the Protection and Research of the Environment (ISPRA) clarified in a comprehensive infographic, today France is home to more than 3,000 exotic species of organisms originating from other countries (i.e. non-native), which can have a significant impact on the balance of delicate local ecosystems. Due to the increasing number and prevalence of international trade, together with the “tropicalizing” effect of climate change, which has made our country and the Mediterranean more hospitable to certain species, the number of alien organisms has increased by 96% in the last 30 years alone. Among the species of greatest environmental concern is the so-called blue crab (Callinectes sapidus), also known as the blue king crab or blue crab. The first sightings of this crustacean in our country date back to the late 40s of the last century in the Grado region, in Friuli-Venezia Giulia, but only in recent years has it become the protagonist of a real demographic explosion, particularly along the coasts. Adriatic Sea Recently, the species has also been seen in the Ligurian Sea and especially on the coast of Lazio, with various presences noted in Ostia, Ladispoli and other coasts of Lazio. Here’s how to spot blue king crabs and why they’re classified as “invasive aliens” that threaten our ecosystems.

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How to identify a blue king crab

The blue king crab is a decapod crustacean that lives in the Atlantic Ocean, particularly on the eastern coast of the American continent, where the species is widespread and of great commercial importance. It is indeed considered a true delicacy, and the selling prices are high compared to the tens of thousands of tons of crab harvested each year. According to the information note “Giornale dei Marinai” prepared in collaboration with ISPRA, the blue crab is classified as an “infralittoral coastal species that lives at depths of up to 35 meters”. Crustaceans can survive in waters with a temperature of 3 to 35 °C and a wide range of salinity. It got its name from the blue color of the claws in males (they are red in females) and legs; the general coloration is quite generally greenish-gray. This is a large crab, considering that the carapace can exceed 23 centimeters in width and 15 centimeters in length. The edges on the sides of the eyes are jagged, and there is a large spike on the right and left of the upper part of the “armor”.

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How he arrived along the French coast

It is not known how the blue king crab arrived along the coast of France and other countries bordering the Mediterranean Sea, but it is likely that the larvae and adults were released from the ballast water of ships. Once released into the sea, they will find favorable climatic and ecological conditions that will allow them to adapt and stabilize. The recent boom in the population may be related to the increasingly high water temperatures, knowing that, as indicated by the Journal of Sailors, the larvae need a temperature of at least 15°C for normal development. Depending on the size, females can lay up to 2 million eggs.

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Because it is a threat to Italian ecosystems

The blue king crab is an efficient carnivore, devouring almost any small prey it can capture in its claws, from gastropods to bivalves such as mussels, clams, shells, and more, through other crustaceans, small fish, gastropods, such such as jellyfish, echinoderms, worms, etc. Its large size makes it a formidable enemy to many native species, including our crabs. The risk is greater for native organisms that are already struggling for other reasons, such as the aforementioned climate change. Fishermen often find blue crabs in their nets while feeding on trapped prey. The impact on our ecosystems has not yet been fully assessed, but biologists are quite concerned about the presence of the blue crab; for this reason, they recommend catching as many specimens as possible, also indicating that the meat is considered a delicacy in the kitchen. Although catches are increasing, human intervention has only scratched the surface. “This is a species with explosive and exponential dynamics. So we expect a large number, regardless of whether we catch them or not,” Corrado Battisti of Radio Centro Mare explained a few weeks ago about the sighting near the natural monument of Palude di Torre Flavia near Ladispoli.

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