Status of alien species in the Mediterranean and Black Sea

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It should be reminded that alien species may carry several parasites or fungi which may threaten native
fauna and flora and thus may cause harm to local fisheries. Therefore they should be monitored by the
riparian governments with national capacity as well as relevant international agencies.
As a consequence of recent climate change and water temperature rise, some Mediterranean species,
such as sardine, bouge and wrasse, have also penetrated into the Black Sea and it is likely that the
fishing catch amount will change in the future. Mediterranean originated species need to be monitored
in the Black Sea. General trends show that a miniature Mediterranean Sea is going to be established
within the Black Sea since several species penetrate to the Blak Sea with various vectors. Besides,
alien species penetration into the Black Sea puts pressure on the autochthonous Black Sea endemic
species. They retreat to the brackish water areas and take refuge in estuaries and deltas. Impacts of the
alien species on the native species may be the loss of ecological niches mostly in the mouths of rivers,
such as the Danube, Dnieper, Dniester, Kizilirmak, Yesilirmak and Sakarya. Because of low salinity
brackish water of the Black Sea, euryhaline and eurytherm species are more suitable to settle.
Due to overfishing, the reduction of total fish biomass in the Black Sea at the end of 1980s to less than
one third of its maximum value in the 1970s has caused a partial emptiness of the occupied ecological
niche. According to the general rule “Natura abhoret vacuum” they were occupied by invader
planktophagous M.leidyi. Overfishing, therefore, should be avoided for all fish species to minimize the
risk of alien species invasion. M.leidyi has already penetrated to the Mediterranean Sea and the lesson
learned in the Black Sea should be applied to the Mediterranean Sea case in terms of impacts on the
fisheries and whole biota.
Public awareness and sensibilization programmes for local people, fishers, boat crew, harbor masters
and coast guards are needed to explain alien species and their impacts on nature, human health and
fisheries. Special education programmes should be given to the fisheries cooperatives to inform local
fishers of the impacts of alien species.
Legal measures for intentional introduction to the Black Sea should be taken by national authorities
and international conventions, such as Bucharest and Bern Conventions. The international cooperation
is essential to combat alien invasive species in the entire ecosystem. The significant impacts of climate
change and Mediterranization should also be taken into account for the Black Sea.