PDF《Part I. Spatial distribution》

128 proven Lessepsian immigrants and

76 doubtful cases (POR, 1978). Since the first review of alien species in the Mediterranean (ZIBROWIUS, 1992), there have been many papers and reviews dealing with this subject. More recently, CIESM has pub- lished four Atlases of Exotic Species in the Mediterranean (GALIL et al., 2002;

GOLANI et al., 2002;

ZENETOS et al., 2004;

VERLAQUE et al., in press). The most recent lists show

116 species of fish- es,

70 species of decapod and stomatopod crustaceans,

137 species of molluscs and

110 species of macrophytes. This increased number of records, particularly over the past few years, has been partly Medit. Mar. Sci., 11/2, 2010, 381-493

382 Abstract The state-of-art on alien species in the Mediterranean Sea is presented, making distinctions among the four subregions defined in the EU Marine Strategy Framework Directive: (i) the Western Mediterranean Sea (WMED);

(ii) the Central Mediterranean Sea (CMED);

(iii) the Adriatic Sea (ADRIA);

and (iv) the Eastern Mediterranean Sea (EMED). The updated checklist (December 2010) of marine alien species within each subregion, along with their acclimatization status and ori- gin, is provided. A total of

955 alien species is known in the Mediterranean, the vast majority of them having being introduced in the EMED (718), less in the WMED (328) and CMED (267) and least in the Adriatic (171). Of these,

535 species (56%) are established in at least one area. Despite the collective effort of experts who attempted in this work, the number of introduced species remains probably underestimated. Excluding microalgae, for which knowledge is still insuffi- cient, aliens have increased the total species richness of the Mediterranean Sea by 5.9%. This figure should not be directly read as an indication of higher biodiversity, as spreading of so many aliens within the basin is possibly causing biotic homogenization. Thermophilic species, i.e. Indo-Pacific, Indian Ocean, Red Sea, Tropical Atlantic, Tropical Pacific, and circum(sub)tropical, account for 88.4% of the introduced species in the EMED, 72.8% in the CMED, 59.3% in the WMED and 56.1% in the Adriatic. Cold water species, i.e. circumboreal, N Atlantic, and N Pacific, make up a small percentage of the introduced species, ranging between 4.2% and 21.6% and being more numerous in the Adriatic and less so in the EMED. Species that are classified as invasive or potentially invasive are

134 in the whole of the Mediter- ranean:

108 are present in the EMED,

75 in the CMED,

53 in the Adriatic and

64 in the WMED. The WMED hosts most invasive macrophytes, whereas the EMED has the lion'

s share in poly- chaetes, crustaceans, molluscs and fish. Keywords: Biological invasions;

Marine aliens;

Biogeography;

Biodiversity;

Mediterranean Sea. attributed to intensification of research effort in this topic. ZENETOS &

POLYCHRONIDIS (2010), based on data gathered, analysed for and adopted in the European Environment Agency (EEA) and UNEP MAP RAC/SPA reports, estimated that nearly

1000 species entered the Mediterranean dur- ing the past century. A recent synthesis on Mediterranean marine biodiversity (COLL et al., 2010) described the Mediterranean Sea as a biodiversity hot spot hosting approxi- mately 17,000 marine species, of which more than

600 (3.3%) are alien. These most recent detailed biodiversity esti- mates for alien species show a discrepan- cy from the figures provided by ZENETOS et al. (2005;

2008). However, as COLL et al. (2010) have pointed out, the true numbers of alien species are cer- tainly biased downwards. The data are presumably accurate for large and con- spicuous species that are easily distin- guished from the native biota and for species that occur along a frequently sam- pled (or fished) coast and for ........