(In both photos: the Atlantic blue crab (Callinectes sapidus) recently caught within Maltese waters for the first time through the Spot the Alien citizen science campaign, showing damage from spearfishing. Photos by Mr Johann Galdies)
The Atlantic blue crab (Callinectes sapidus), native to the western Atlantic Ocean and the Gulf of Mexico, listed as one of the worst invasive species introduced to the Mediterranean, has been recorded for the first time from Maltese waters by the Spot the Alien citizen science campaign. This omnivore crab species was first recorded from the Mediterranean in the 1940s from the Adriatic and hence since then established large populations throughout the Mediterranean, although it had not been recorded to date from Maltese waters. It is taught that the species was introduced to European and to Japanese waters through shipping ballast waters, a major vector for the spread of marine alien species worldwide.
The species is edible and is actively fished along most of the Atlantic coast of the US, representing a 200-million-dollar fisheries industry. In the Mediterranean, C. sapidus in consumed on a large scale in a number of countries, including Greece. Interestingly enough, the single C. sapidus individual fished recently from Maltese waters was caught along with a number of blue swimmer crab (Portunus segnis) individuals. The latter is yet another invasive crab species, native of the Indian-Pacific Ocean region, and firmly established within Maltese waters, especially along the eastern coastline of the islands. P. segnis is regularly consumed locally, being even sold at fish markets and in restaurants and even being imported in a frozen fashion from Tunisia.
The Spot the Alien citizen science campaign is coordinated by Prof. Alan Deidun, resident academic within the Department of Geosciences of the Faculty of Science and Ocean Ambassador for Malta, being financially supported by the International Ocean Institute (IOI).
Prof. Deidun is assisted in the running of the campaign by resident academic Dr Adam Gauci and by Mr Johann Galdies. Along with the Spot the Alien Fish and Spot the Jellyfish campaigns, which are also coordinated by the Department of Geosciences, this citizen science programme has managed in recent years to document, as an Early Warning system, a considerable number of non-native species for the first time from Maltese waters, including the flat needlefish (Ablennes hians), the Queen and the Guinea Angelfish (Holacanthus ciliaris and Holacanthus africanus), the silver-cheeked toadfish (Lagocephalus sceleratus), the Azure demoiselle (Chrysiptera hemicyanea), the Red Sea mantis shrimp (Erugosquilla massavensis), species belonging to the ascidian genus Symplegma and the flatworm Maritigrella fuscopunctata, besides a number of alien jellyfish species, including the Australian spotted jellyfish (Phyllorhiza punctata) and the nomadic jellyfish (Rhopilema nomadica), besides a bonanza of previously-unrecorded siphonophore species (e.g. barbed-wire jellyfish, hula skirt siphonophore).
According to Prof. Deidun, it is still too early to anticipate whether the Atlantic blue crab will proliferate in local waters in a similar fashion to the blue swimmer crab, although the introduction of this second invasive crab species to our waters is definitely a cause for concern. A scientific paper detailing this latest discovery from Maltese waters has been submitted for review to a high-impact journal and should be openly available once such a review process has been completed. Through the completed HARMONY project, funded within the Interreg Italia-Malta 2014-2020 Programme, the Department of Geosciences commissioned a short animation clip on the key messages concerning Invasive Alien Species, which can be viewed below: