Status of alien species in the Mediterranean and Black Sea

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The changes in the Black Sea ecosystem that have occurred since the 1960s due to the concurrent
impacts of eutrophication, overfishing, climatic fluctuation and alien species invasions have been
studied extensively. A synthesis provided recently in State of the Environment Report (BSC, 2008)
examines the changes in pelagic and benthic ecosystems.
The Black Sea’s biodiversity clearly reflects its geological history. Brackish water fauna known as
“Caspian relics” originated from the Neoeuxinian Lake, and the components of this fauna are found
only in waters with low salinity. Some bivalves, such as Dressenia, and fishes, such as gobies and
sturgeons, are good examples. Another group of species is called “cold water relics” and includes
ctenophores (Pleurobrachia), copepods (Calanus), and fishes such as spiny dog fish, sprat, flounder
and whiting (Zaitsev and Mamaev, 1997), (Öztürk and Öztürk, 2005). This group is the second oldest
inhabitants of the Black Sea, entering the sea between the Neoeuxine Lake Period and the early stage
of the formation of the Istanbul Strait (Bosphorus). After the Istanbul Strait (Bosphorus) established a
connection with the Mediterranean Sea about 7 000–10 000 years ago, the salinity of the Black Sea
rose gradually and soon the Mediterranean species were established in the Black Sea. Today, 80
percent of total fauna in the Black Sea is of Mediterranean origin. According to Slastenenko (1959),
the Black Sea received more than one third and about one fifth of its fauna from the Aegean Sea and
the Mediterranean Sea, respectively. The last group of species is called “alien species”, which includes
those introduced either intentionally or unintentionally by human activities from the various seas and
oceans of the world.
1.2 Vectors for the alien species in the Black Sea
In recent years, the Black Sea has become home for a large number of alien plants and animals. There
are three main vectors for alien species to reach the Black Sea. These are: a) shipping activities, which
is the most common way; b) intentional or unintentional introduction by humans; c) Mediterranization,
which means that Mediterranean originated species pass all ecological barriers in the Turkish Straits
and penetrate to the Black Sea.
1.2.1 Shipping activities
The most common way of invasion of alien species is via ocean-going ships. Marine organisms
usually travel either as a part of the fouling attached to ship hulls either in tank sediment or in ballast
water. (Zaitsev and Mamaev, 1997; Zaitsev and Öztürk, 2001; Öztürk 2002a;b; Gomiou et al., 2002;
Streftaris et al., 2005). Shipping activities are intense in the Black Sea mainly due to the Caspian
petrol transportation from Novorossisk, the Russian Federation, to the Mediterranean countries via
Turkish Straits (Figure 3). It is also known that the largest unintentional pathway for the transport of
marine organisms is the ballast water of commercial vessels and a typical commercial bulk vessel may
carry over 30 000 metric tonnes of ballast water to provide stability and trim adjustment during a
voyage (cited in Wonham et al., 2000).
Hundreds of algal and animal species, both microorganisms and even smaller organisms, are known to
travel by attaching themselves to the hulls of the ship. Most of them are attached to the living substrate
such as algae, clams and barnacles. However active non-sessile forms can also be found, such as
amphipods, shrimps, crabs and fishes. When the ship is in motion they hide in barnacles and other
similar shelters, so as not to be swept away by the current.
Ballast water pumped to tanks to stabilize a ship when it is not carrying any cargo. When ships fill
their ballast tanks in ports or sometimes in certain areas, suspended matter and various planktonic
organisms are also pumped into the tanks with the water. Many organisms survive the trip in the
ballast water or sediment, sometimes as spores and eggs. Upon arrival at the ship’s destination, the
ballast water is discharged into the sea and the organisms find themselves in a new environment. If the