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Alien crabs in the Mediterranean Sea: current status and perspectives

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Dimitris Klaoudatos , Kostas Kapiris
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Hellenic Centre for Marine Research, Institute of Marine Biological Resources, 47 km Athens-Sounio,
Mavro Lithari P.O. Box 712, 19013, Anavissos, Attica, Greece
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e-mail: dklaoudatos@hcmr.gr, kkapir@hcmr.gr

Abstract
Biological invasions are recognized worldwide as an important element of global
change. The Mediterranean Sea a semi-enclosed, deep, oligotrophic basin is one of
the seas most affected by biological invasions in terms of duration of invader’s
presence, number of alien species detected and the unprecedented rate of
introduction.
The opening of the Suez Canal in 1869 had serious zoogeographically and
ecologically affected both Red Sea and the Mediterranean Sea, with different
faunistic and hydrographic attributes, tropical Indo-Pacific origin the first, temperate
the second one. The impacts of invasive species on their new environment include
the restructuring of established food webs, competition with native organisms,
alteration of gene pool, extinctions, and introduction of new diseases.
The total number of the alien species in the Mediterranean (2012) was 986
species (775 in the eastern Mediterranean, 249 in the central Mediterranean, 190 in
the Adriatic Sea and 308 in the western Mediterranean). The native range of the
alien species in the Mediterranean is most commonly the Indo-Pacific Ocean (40%),
the Indian Ocean (17%), the Red Sea (11%) and pantropical (9%). The majority of
aliens in the easternmost Mediterranean have entered through the Suez Canal (68%,
15% vessel-transported, 2% mariculture), whereas mariculture (43%) and vessels
(37%) are the main means of introduction in the western Mediterranean.
The alien decapod fauna in the Mediterranean has lessepsian and Atlantic
origin. Approximately 77% of all alien Mediterranean decapod species have an Indo-
Pacific/Indian/Red Sea origin, while only 23% are from the Atlantic. The biggest
number of the alien decapods (82%) is located in the eastern part of the
Mediterranean in comparison to the western one. The increasing number of the
alien species in the last years could be attributed mainly to the increasing passage of
vessels through the Suez Canal, the development of mariculture and other
anthropogenic pressures.
A number of 39 alien Brachyura species of Red Sea/Indo-Pacific origin,
belonging to 19 families, have been recorded in the Mediterranean Sea, mainly in
the eastern part. In this area, the pathway of introduction of decapods species is the
Suez Canal, but penetration has been either unintentional (Lessepsian migration) or
ship-mediated. The families Portunidae, Pilumnidae and Leucosiidae show the
highest number of Red Sea/ Indo-Pacific aliens, while the remaining families are
represented by only one or two species.
The most known invader crabs in the Mediterranean are: Portunus pelagicus
and Percnon gibbesi which are the most recent and successful invaders in the
Mediterranean Sea. The blue crab Callinectes sapidus was transported into the

∗ Corresponding author