Fate of the Black Sea Acartia clausi and Acartia tonsa (Copepoda) penetrating into the Marmara Sea through the Bosphorus

In October 2005 spatial distribution of live and dead Acartia clausi and Acartia tonsa was studied in the Black and Marmara Seas and near the Marmara Sea inlet of the Bosphorus, in order to understand their fate upon transportation between two seas. The morphometric characteristics in both species from all studied areas, and the decreased abundance of A. clausi and A. tonsa from the Black Sea towards the Marmara Sea indicate that the Marmara Sea Acartia populations are formed by recruitment from the Black Sea. We observed mass mortality of A. clausi in the Marmara Sea near the Prince Islands. The majority of carcasses (66% of total A. clausi numbers in the Marmara Sea) were found in the salinity gradient layer. Laboratory experiments showed that during a gradual salinity increase (3.5–4 h) from 18.9 (salinity of the Marmara Sea surface layers) to 39.8 (Marmara Sea salinity at depths >25 m) Acartia clausi began to die at a salinity of 30 and that all copepods were dead at 39.8. In comparison with A. clausi, Acartia tonsa was more tolerant to short-term salinity increase. Despite the high salinity tolerance of A. tonsa however, the abundance of this species was estimated to be very low in the offshore Marmara Sea. Respiration rate and frequency of jumps in A. tonsa were 1.3–1.5 and 1.77 times higher, respectively, than those in A. clausi.