Dynamics of Noctiluca scintillans (Macartney) Kofoid & Swezy and its Contribution to Mesozooplankton in the Southeastern Black Sea

During the last half century, significant changes have been observed in the zooplankton communities in the Black Sea. While some species have almost disappeared, someother species have increased in number. Noctiluca scintillans is a red-tide forming heterotrophic dinoflagellate, which is widely distributed in the world's oceans. Due to its large cell size (>200 mu m) and phagotrophic feeding behavior, Noctiluca scintillans is assessed within mesozooplankton communities. After the 1970s, Noctiluca scintillans became dominant in the mesozooplankton community in the Black Sea. Between May 2015 and April 2016, the population characteristics of Noctiluca scintillans and its contribution to mesozooplankton communities were investigated in surface waters in the southeastern Black Sea. The abundance of Noctiluca scintillans in surface waters ranged between 0-23357 cells/m(-3) with the lowest number found in the summer and the highest number found from February to May. Abundance tended to increase from the river mouth toward open waters. During the study, the cell diameter and volume of Noctiluca scintillans varied between 352-629 mu m and 2.28 x 10(7)-1.3x10(8) mu m(3), respectively. The total mesozooplankton abundance ranged between 10-24020 individuals/m(-3). There are no statistically significant differences in Noctiluca scintillans and mesozooplankton abundance between sampling stations (p>0.05). The contribution of Noctiluca scintillans to the mesozooplankton population was the lowest during summer, but from February to May, Noctiluca scintillans comprised 79%+/- 4% and 98%+/- 2% of the total mesozooplankton population in the river mouth and coastal waters, respectively. These results confirm that Noctiluca scintillans is still an important contributor of the mesozoplankton community in the southeastern Black Sea.