Blue crabs and other aliens: the era of invasive species
The spread of this Atlantic species threatens biodiversity, as well as the economy and tourism of Mediterranean countries. But, it is not the only unwanted guest: according to a report published by IPBES, alien invasive species cost humans $423 billion each year.
Their deeds filled the summer newspapers: voracious, prolific and robust, the Atlantic blue crab (Callinectes sapidus) is conquering the seas and rivers of Mediterranean countries. Although the first reports of this crustacean, hailing from the Atlantic coasts of the Americas, date back to the middle of the last century, climate change and the intensification of maritime traffic has boosted their success in recent years.
However, this is not good news: the spread of the blue crab threatens biodiversity, as well as the economy and tourism. Blue crabs are larger and more aggressive than most other Mediterranean crabs and, until now, they do not face specialised predators. They disrupt bottom habitats, shred fishers’ nets and ruin their catches. To make matters worse, the invasion is taking place on multiple fronts because the species of blue crabs settling in the Mediterranean are, at least, two.
Coming from the western Indian Ocean, the African blue swimming crab (Portunus segnis) reached the Mare Magnum at the beginning of the last century through the isthmus of Suez. Their behaviour and biology — as well as their impact — are similar to those of the Atlantic species but P. segnis are also good swimmers.
“The Mediterranean sea is a hotspot of biological invasions. Roughly speaking, it is estimated that a new species is observed every two weeks. Most of them are invertebrates or belong to primary producers” says Momme Butenschön, lead scientist of the Research Unit for Earth System Modelling of the Euro-Mediterranean Center on Climate Change.
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