In May-June 2005 in the northeastern Black Sea, on its shelf, slope, and in the open sea, intensive (up to 1.92x10⁵ cells/L) growth of alien species, Chaetoceros throndsenii (Marino, Montresor & Zingone) Marino, Montresor & Zingone was observed. At the same time, a mass development of coccolithophore Emiliania huxleyi (Lohm.) Hay et Mohl. took place, cell numbers of which reached the level of blooms. The experimental studies of natural phytoplankton community have shown that the synchronous nitrogen and phosphorus supply promoted intensive growth of Ch. throndsenii. A complete removal of this species’ cells in the continuous (chemostat) culture took place when a dilution rate was 0.25 day^-1. When the dilution rate was 0.15 day^-1 short-term (7 days) coexistence of Ch. throndsenii and Pseudo-nitzschia pseudodelicatissima (Hasle) Hasle was observed. The maximal growth rate of new species in continuous culture was recorded during the first three days at was 1.4 day^-1. A maximal cell degradation of Ch. throndsenii (0.5 day^-1) was recorded in the last phase of the bath culture with the synchronous nitrogen and phosphorus supply. A low rate of water exchange in the surface mixed layer (< 0.15 day^-1), stable stratification and relatively small nitrogen and phosphorus concentrations are necessary for appearance and long existence of this alien species in the Black Sea.

Keywords: alien species, Chaetoceros throndsenii, coccolithophores, nitrogen, phosphorus, phytoplankton

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