Structure of Plankton Phytocoenoses in the Shelf Waters of the Northeastern Black Sea during the Emiliania huxleyi Bloom in

It is shown that, in , the mass development of the coccolithofore Emiliania huxleyi on the Gelendzhik shelf occurred annually and in May-June its abundance reached 1.5 [image] 10 super(6)cells/l. In , the bloom of E. huxleyi was accompanied by a mass development of the diatom alga Chaetoceros subtilis var. abnormis f. simplex (0.6-0.9 [image] 10 super(6) cells/l); for the first time, it was registered as a dominating form of the Black Sea phytoplankton. Small flagellates and picoplankton algae played a noticeable role in the phytoplankton throughout the entire period of the studies. Meanwhile, in the early summer period, the bulk of the biomass consisted of coccolithophores (50-60%), while, in the late summer period, diatomaceous algae dominated (50-70%). Among the ecological factors that favor the coccolithophore development one may note the microstratification of the upper mixed layer at a high illumination level and high temperature in the surface waters (18-21 degree C). The terrigenous runoff during the rainy period had a negative effect on the E. huxleyi development, while storms dispersed the population over the upper mixed layer. The wind-induced near- shore upwelling stimulated the development of diatoms.