Status of alien species in the Mediterranean and Black Sea

45
Mediterranean ichthyofauna and the increase of 20 percent within four years only. Zenetos et al.
(2007) updated the number of alien species in Greek waters as increased from 102 to 110. Out of the
eight new records, five are zoobenthic species, two zooplanktonic and one is a teleost fish. Ergüden et
al. (2009) studied the weight-length relationship for 20 lessepsian fish species in the Eastern
Mediterranean. Yokes et al. (2009) pointed out that Vanderhorstia mertensi (Klausewitz, 1974), is a
recently acknowledged alien fish in Fethiye Bay and that its population has increased rapidly.
Dispersion of the lessepsian fish in the Mediterranean Sea depends on several factors such as cyclonic
Mediterranean shore currents to the Levantine Sea, and similar temperature conditions. Most of the
successful species are euryterm and euryhaline species and they can adapt to other ecological
conditions such as feeding and habitat type (Mavruk and Avşar, 2008). Gücü and Gücü (2002)
reported that low native species diversity was affecting the rate and the success of immigrant
colonization. Furthermore, the absence of Posidonia oceanica meadows was found to be another
important factor, affecting the success of lessepsian invasion. P. oceanica, the endemic seagrass that is
the key species of the Mediterranean coastal ecosystem, was found responsible for defending the
Levant Sea’s ecological integrity and its native characteristics against invasion. Its absence has
resulted in a successful invasion of lessepsian species.
In Appendix 3, alien fish species are listed according to various sources including Websites such as
www.ciesm.org, www.fishbase.org, Oral (2010), Lasram-Rais and Mouillot (2009).
Marttin et al. (2006) widely examined the fisheries sector in the eastern Mediterranean under the
MEDFISIS Project and they found that the abundance of some native species has declined while that
there has been an increased abundance of lessepsian species. Competition within the same ecological
niche and the direct interference could be possible explanations for the successful colonization (Golen
and Galil, 2005). It has been reported that the increasing exploitation of non-native species caused a
shift of the trawl fishing ground towards shallower waters where their biomass density is highest (i.e.
at bottom depth up to 50 m), and a consequent increase of the ratio of non-native to native species in
Levantine trawl landings (Pisanti and Grofit, 1991). Marttin et al. (2006) listed the species
successfully established and commercially important in Levantine fisheries according to the CIESM
exotic species book and seven fish and three crustacean species were reported as commercially
exploitable alien species from the Eastern Mediterranean Sea.
The vertical distribution of lessepsian fish species has also been examined by several authors.
Bilecenoğlu and Taşkavak (2002) reported that a few specimens of Upeneus moluccensis were found
at a depth of 180–190 m in the Turkish coasts and that this species seemed to be very adaptive to the
low temperatures prevailing in such depths throughout the eastern Levantine Basin. Similarly, Golani
(1996) found some species at a depth of 200 m off the coast of Ashdod in Israel. As a matter of fact,
lessepsian fish has higher mobility as opposed to most invertebrates and the majority of the fish
species found at 20–40 m depth as stated by Por (1978). But bathymetric distribution changes below
70 m, which has a threshold effect as a limiting factor due to low temperature occupation of the
circumlittoral zone.
Lessepsian fish migrants are also utilized for several purposes like aquaculture, aquarium, game fish
and as bait in the fishing industry (see Table 3.2).