Status of alien species in the Mediterranean and Black Sea

EXECUTIVE SUMMARY
9
Biota of the Black and Mediterranean Seas have started to change with the introduction of alien
species in the last few decades due to lessepsian migration, Atlantic influx, intentionally or
unintentionally introduction and climate change. The dispersion of alien species is a dynamic process
that shows an increasing trend and is likely to continue in the future. This phenomenon causes severe
ecological, socio-economical and human health problems in the entire basin.
Shipping and intentional introduction are the main vectors of alien species introduction to the Black
Sea. In the Black Sea, several alien species dispersed and caused threats to the native biota due to the
low biodiversity and a character as an enclosed sea. A comb jelly, Mnemiopsis leidyi, which was
transported to the Black Sea with ship ballast water and caused ecological impacts and economical
damages to the riparian countries’ fisheries due to feeding of mostly the larvae and eggs of small
pelagic fishes, mainly anchovy, horse mackerel and spratt. A gastropod, Rapana venosa, is the first
alien commercial species in the Black Sea and after 1980s it became an export product for all the
Black Sea countries. Meanwhile, its impact on the native fauna, especially on mussel and oyster beds,
was detrimental.
Mediterranization is also a growing trend and many Mediterranean origin species have penetrated to
the Black Sea, even a stinging compass jelly fish, Chrysaora hysoscella. Recently, lessepsian fish
migrants such as blunt barracuda Sphyraena pinguis and a coral-dwelling fish, Heniochus acuminatus,
had been reported for the first time. On the contrary, an intentionally introduced species, Liza
haematocheila, penetrated to the Aegean and Mediterranean Sea through Turkish Straits. It shows that
these two basins are closely interacting with each other.
The Marmara Sea is a link between the Black and Mediterranean Seas and serves as a biological
corridor, an acclimization area and a barrier for alien species. M. leidyi had also a detrimental effect on
anchovy fisheries in the Marmara Sea and the recovery of the stocks has started in the recent years.
Poisonous lessepsian fish migrant, Legocephalus scelaratus, and an alien stomatopod shrimp,
Erugosquilla massavensis, have also been reported in the Marmara Sea recently. Shiping is the main
vector for alien species in the Marmara Sea.
As for the Mediterranean Sea, alien species enter from the Atlantic Ocean through the Gibraltar Strait,
the Red Sea through the Suez Canal, from the Black Sea through the Canakkale Strait (Dardanelles)
and by intentional or unintentional introduction. Some lessepsian sprinter fish species pass the Sicily
Strait which is known as a biogeographical boundary between the eastern and western Mediterranean
Sea. On the other hand, some species of Atlantic-origin penetrated into the Mediterranean Sea farther
east reaching the coast of Sicily from the originally established areas near the Gibraltar Strait.
The main vectors of the Mediterranean alien species are the Suez Canal, shipping and aquaculture. A
general trend shows that the number of alien species has increased in recent years but the number itself
is debatable. Nevertheless, alien species are increasing regional marine biodiversity in the Black and
Mediterranean Seas.
Alien species have had several consequences on fisheries, biodiversity, human health and economy in
the Mediterranean Sea. Some of the alien fish species have become economically important after the
establishment of sustainable populations, such as lizard fish, goatfishes, Spanish mackerel and round
herring mostly in the eastern Mediterranean region. Similarly some of the crustacean species are also
commercially important, such as kuruma prawn, green tiger prawn, mantis shrimp, swimming crabs,
and blue crabs. Some introduced mollusc species, such as the Japanese oyster and Pacific carpet clam,
already have a market value. Besides, some species have negative impacts on human health, mostly
puffer fishes, Legocephalus spp., an alien jellyfish, Rhopilema nomadica, and a hydroid, white stinger,
Macrorhynchia philippina, in the eastern Mediterranean countries. The eradication of Caulerpa
taxifolia and Caulerpa racemosa negatively impact the fisheries and ecosystem in the Mediterranean
Sea. Some species badly affect fishing gears by causing mesh clogging, fouling and damaging. Some