An Unusual Red-Tide Event of Noctiluca Scintillans (Macartney) in the Southeastern Black Sea

An intense Noctiluca scintillans bloom is reported for the first time in the southeastern coast of the Black Sea. During the present study, surface water samples were collected in the vicinity of the port of Rize between 18 and 20 April 2011. The bloom appeared as a sudden increase in cell number (6.81 x 106 cells l-1) and persisted during three days. The bloom led to a red-tide event with typical streaks and patches of reddish viscous surface waters. The abundance of Noctiluca was higher than other previous reports in the Black Sea. During the bloom, sea surface temperature ranged between 9.9-11.7 degrees C and salinity ranged between 15.04-17.7 %. Nitrite+nitrate, silicate and phosphate concentrations ranged between 0.59-7.13 mu M l-1, 3.69-10.92 mu M l-1 and 0.04-0.19 mu M l-1, respectively. Meteorological data showed light precipitation and low wind speed before and during the red-tide, indicating a stable stratified surface environment, optimum for the red-tide initiation. Light onshore winds may have caused accumulation of cells near the coast and possibly also contributing for triggering the red-tide. The abundance of N. scintillans correlated positively with chl-a concentration (R2=0.83) and an intense bloom of diatom Melosira spp. (5x105 cells l-1) was found concomitantly with N. scintillans red-tide. Microscopic examination of live cells from the N. scintillans red-tide revealed the presence of high number of Melosira spp. within the N. scintillans body, confirmating its grazing on these microalgae. The occurrence of this anomalous event may indicate a shift in the planktonic food web as a result of natural variability or anthropogenic influences like eutrophication.