Abstract:

The Sea of Marmara is under the influence of the Black Sea and the Mediterranean. The salinity difference between these two seas causes the formation of two-layer stratification in the Sea of Marmara, an upper layer formed by the fresh waters of the Black Sea and a denser layer formed below 25 m of depth, by the more saline waters of the Mediterranean. The salinity difference, together with the seasonally changing meteorological events are the major factors which shape the main current system. The Mediterranean waters enter the Dardanelles cross the Sea of Marmara and flows into the Black Sea via İstanbul Strait, which enables the dispersion of the alien foraminifer species already established on the Aegean coasts into the Sea of Marmara. Besides, the Sea of Marmara includes important harbors, suggesting that there is an extensive pressure of alien species introduced by ballast waters. In this study, 322 sediment samples, obtained from different localities in Dardanelles, İstanbul Strait and Sea of Marmara, were investigated for the alien foraminifer species. The results are combined with the previous records in the literature for creating an alien foraminifer checklist for the Sea of Marmara. 10 alien foraminifer species belonging to 9 genera were found in Dardanelles, 32 alien species from 28 genera in the Sea of Marmara, and only 2 alien species from 2 genera were found in İstanbul Strait. Majority of these alien species have Indo-Pacific or Atlantic origin, suggesting that shipping may be the most possible mode of introduction. But it is also observed that some of the Indo-Pacific originated species which were introduced Suez Canal and formed established populations along the Turkish coastline are also found in Dardanelles, indicating that major currents systems are also playing a role in the dispersion patterns of the alien foraminifers in the Sea of Marmara. Another important factor may be the thermal submarine springs found on the bottom of the Sea of Marmara, which may create suitable environmental conditions and enhance the establishment of thermophilic alien species. 

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