Status of alien species in the Mediterranean and Black Sea

Öztürk, B.
Status of alien species in the Black and Mediterranean Seas.
Studies and Reviews. General Fisheries Commission for the Mediterranean. No. 87. Rome, FAO.
2010. XXp.
iv
ABSTRACT
This study, undertaken upon request by the General Fisheries Commission for the Mediteranean
(GFCM), summarizes the available information about the status of alien species in the Mediterranean
Sea and the Black Sea.
The biota of the Black and Mediterranean Seas has started to change with the introduction of alien
species in the last few decades due to increasing shipping activities, lessepsian migration, Atlantic
influx, intentional or unintentional introduction as well as climate change.
The Black Sea suffered from the alien combjelly Mnemiopsis leidyi for long years since the late
1980’s in terms of biodiversity and decrease in fish catch, mostly of small pelagic fish such as
anchovy. Mediterranization is also a growing trend and many Mediterranean origin species have
penetrated to the Black Sea, most probably due to climate change in recent years. On the other hand, a
sea snail, Rapana venosa, is the most commercial alien species harvested by the Black Sea countries.
The Sea of Marmara has crucial importance between the Black and Aegean Sea due to the exchange of
water mass and marine biota. The Sea of Marmara was also negatively impacted by the combjelly
Mnemiopsis leidyi with the recovery taking place in terms of small pelagic fish only in recent years.
Lessepsian fish and invertebrates are increasing in the Sea of Marmara but overall impacts are not yet
known. Rapana venosa has been commercially exploited also in the Sea of Marmara.
The Eastern Mediterranean Sea has been invaded by numerous lessepsian species entering through the
Suez Canal. Some, not all, lessepisan species are found in the Central and Western Mediterranean Sea.
Marine Protected Areas and protecting native species can be effective for mitigating negative impacts
of the invasion of alien species. Furthermore, as a consequence of the increase in populations of
lessepsian species, consumption of some of such species has been started and they are influencing the
local market mostly in the eastern Mediterranean region. This new market of alien species shows an
increasing trend. Some alien species have negative impacts on human health, tourism and fisheries,
such as puffer fishes and jellyfish, and need to be particularly monitored. Important impacts on the
biodiversity are already reported especially in the eastern Mediterranean Sea as habitat displacement
and competition with native species.
In total, over 900 species are alien species in the Black and Mediterranean Seas. Various fishing
techniques such as trawling, purse seining, setnets, gillnets and pots are used for alien species fishery.
Due to lack of overall statistics, total catch in the entire basin is not known and not predictable. Some
of alien fishes which do not have commercial value, such as pufferfish and cornetfish, are discards.
Some Atlantic orginated fish and invertabrate have also extended to the eastern part of the
Mediterranean Sea. Besides, ship ballast water and intentional and unintentional introduction are
growing threats for marine biodiversity in both basins.
Information dissemination and raising public awareness mostly for harmful species is important on a
regional level. Regional cooperation for monitoring and protecting marine bioidversity is essential to
minimize and reduce the impacts of alien species both in the Black and Mediterranean Seas. Besides,
the enforcement of the legal measures is also necessary to reduce the introduction of alien species.