Patterns of vertical distribution of dinoflagellate populations with heterotrophic and mixotrophic types of nutrition were studied in the open waters of the Black Sea during September-October 1992. Population of Ceratium fusus dominated in the dinoflagellates; it consisted of cells with both autotrophic and heterotrophic types of nutrition. In the heterotrophic part of phytoplankton Pronoctiluca pelagica and heterotrophic cells of Ceratium fusus dominated. The major part of these two populations occurred in the layer of thermocline, while another significant part occupied the upper mixed layer. One maximum of P. pelagica was located in the layer of thermocline and usually coincided with location of the biomass maximum of autotrophic cells of C. fusus. Two peaks were typical for vertical profiles of heterotrophic C. fusus: the upper one in the 0-20 m layer and the lower one at 15-45 m. Maximum biomass values of other heterotrophic dinoflagellates were observed in the upper mixed layer. These maxima, in parallel with the upper peak of biomass of heterotrophic C. fusus, coincided with aggregations of autotrophic diatom Rhizosolenia calcar-avis. Spatial niche inhabited by heterotrophic dinoflagellates was significantly more expanded over depth (0-50 m) as compared with autotrophic algae (0-30 m). Positive correlation was observed between biomass values of R. calcar-avis and autotrophic cells of C. fusus. On the contrary, percentage of heterotrophic cells in the population of C. fusus was inversely related to contents of phosphates and nitrates in the cold intermediate layer. This indicates that the ratio between autotrophic and heterotrophic compounds of the population depends on penetration of nutrients from the lower layers to the euphotic zone.

Supplement to: Mikaelyan, A S; Zav'yalova, T A (1999): Vertical distribution of heterotrophic phytoplankton in the Black Sea during the summer period. Translated from Okeanologiya, 1999, 39(6), 895-902, Oceanology, 39(6), 813-820