The , coordinated by the Oceanography Malta Research Group within the Department of Geosciences of the Faculty of Science, has recently added two further marine NIS (Non-Indigenous Species) to the growing list of such species for Maltese waters. The species in question are both crabs, namely the Atlantic blue crab (Callinectes sapidus) and the Indo-Pacific swimming crab (also known through the common name of ‘spiny hands’) Charybdis helleri.
The Atlantic blue crab is native of the western Atlantic (Canada all the way to northern Argentina) and is listed among the worst invasive species introduced into the Mediterranean. A single individual of the species was caught in Marsaxlokk in July 2021 and was reported to the Spot the Alien citizen science campaign. This species was first detected in the north Adriatic Sea at the end of the 1940s, introduced probably via ballast waters and/or for aquaculture purposes. To date, this crab has been recorded from almost the entire Mediterranean basin, except for a few regions, including, until recently, the Maltese Islands. Due to its abundance, edible nature and sheer dimensions, C. sapidus already represents an exploitable fisheries resource in many Mediterranean countries. The Atlantic blue crab is known as an euryhaline species, tolerant of a broad range of salinities, occurring in both marine, estuarine/brackish and freshwater environments. For instance, within the Mediterranean, this invasive portunid crab has colonised extensive swathes of the Ebro River and inhabits many coastal lagoons of the basin, such as lagoons in Tunisia, Greece, Egypt, while it has also been recently reported for the first time from a Libyan coastal lagoon.
The Indo-Pacific swimming crab is reputed to have a circum-global distribution within warm waters. The decapod species, native to the Indian-West Pacific region, was first recorded from the Mediterranean along the Israeli coast in 1924 and, to date, its Mediterranean distribution has been restricted to Levantine waters. A single individual of the species was caught in August 2021 off Vittoriosa in the Grand Harbour and was reported to the Spot the Alien campaign.
The Spot the Alien citizen science campaign is encouraging the general public, as well as Maltese and Gozitan fishers and divers to report any sightings of marine invasive species, and in doing so, better informing scientists to get a better idea and a more accurate picture of just how wide these species are spreading across Maltese waters.
This is not the only citizen science campaign to gather nationwide attention, with another two campaigns, namely the and the Spot the Alien Fish campaign also welcoming contributions from the public under the coordination of Prof. Alan Deidun and with the contribution of Dr Adam Gauci, Dr Joel Azzopardi, Mr Johann Galdies and Mr Alessio Marrone. In fact, within the Spot the Alien Fish citizen science campaign, an underwater camera is also being offered as an incentive to whoever has the first verified sighting of the lionfish in Maltese waters. The three campaigns have jointly recorded around 20 new species for Maltese waters over the past decade and are actively collaborating with corresponding citizen science networks within North Africa so as to bridge any knowledge and data gaps on marine alien species within such a region.
The two scientific publications in question can be consulted through these links:
The first confirmed record of the Atlantic blue crab Callinectes sapidus Rathbun, 1896 (Decapoda, Brachyura) from Maltese waters and
New alien Mediterranean biodiversity records (November 2021)
