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The increasing importance of non indigenous species is particularly evident
for the Central Mediterranean Sea, which separates the western from the eastern
sectors of the basin. In this subregion shipping is the main pathway that accounts for
the introduction of most species. (Zenetos et al., 2012).
The observed increased trend in new introductions by shipping is not
expected to halt unless effective measures are taken. Trends in new introductions of
alien species by shipping are expected to decrease only when the ‘International
Convention for the Control and Management of Ships’ Ballast Water and Sediments’
(BWM Convention) becomes legally binding, by substantially reducing the transfer of
marine species via ballast water. Nevertheless, introductions by hull-fouling will
remain. (Zenetos et al., 2012).
Introduction of non indigenous species through aquaculture is apparently
slowing down. In the last decade, aquaculture has been responsible for 14 new non
indigenous species in the Mediterranean vs 18 species in the previous two decades
1981-1990 and 1991-2000, but new non indigenous species continue to appear in
the vicinity of oyster farms (M. Verlaque and F. Mineur, unpubl. data).
While maritime traffic and other human activities such as aquaculture are
important vectors for the introduction of alien species worldwide (Ruiz et al., 2000),
in the Mediterranean they are not the main reasons responsible for the large
differences observed among the four basins. In the Eastern Mediterranean, the
human intervention responsible for most of the aliens is the reestablishment of the
connection with the Indo-Pacific through the Suez Canal (1869), rather than the
actual transfer of the invaders. In addition, with the present climate change (Belkin,
2009), the tropical features and temperature of the waters are increasing more
quickly in the Eastern Mediterranean, implying dramatic modifications of the biota
(Por 2009, 2010). As a consequence, Indo-Pacific species (regardless of the mode
introduction) have found optimal environment for settlement in the Eastern
Mediterranean.
On the contrary, the Adriatic Sea, which is topographically a dead end,
comprises the area with the lowest number of aliens, receiving them among those
already established in the Eastern Mediterranean and Central Mediterranean that
spread northwards, or among those introduced via shipping or aquaculture in hot
spot areas such as the Venice Lagoon (Occhipinti-Ambrogi et al., 2010).
The list of exotic animals and plants that invaded the Mediterranean is
getting longer every day (Zibrowius, 1991; Ribera and Boudouresque, 1995). Besides
the afore-mentioned Lessepsian migrations, species are intentionally or accidentally
introduced into the Mediterranean via ship fouling, ballast waters, aquaculture,
trade of living bait, wrapping of fresh seafood with living algae, aquariology, and
even scientific research.
The principal pathway of crustacean introduction varies according to the
subregion. In the Eastern Mediterranean Sea almost 80% are derived from the Indo-
Paciic through the Suez Canal, although in some cases these inputs can be dual
(corridors and shipping, either in ballast water or among hull fouling) or even caused
by aquaculture. In the Western Mediterranean Sea the situation is different, as a
considerable proportion of non indigenous species (between 57% and 71%) has been
introduced by shipping, 24% to 33% used corridors as a primary pathway (Suez
Canal, and in a few cases inland canals), and only 10% to 14% can be linked to