Structural and functional parameters of the Black Sea phytoplankton during the summer bloom of the coccolithophore Emiliania huxleyi

Abstract

The aim of the study was to examine the main primary production indicators, describe the controlling factors and identify the conditions for the weak bloom of Emiliania huxleyi in the Crimea coast of the Black Sea during June – July 2022. The surface chlorophyll a (Chl a) varied between 0.3 to 1.5mgm-3 and primary production (PP) within 12–174mgC m-3 day-1. The integrated concentration of Chl a in the euphotic layer was 4–29mgm-2, and that of PP - 240–835mgC m-3 day-1. On average, 49% of Chl a was located bellow the photosynthetic zone. The relationship between integral PP and the total Chl a, nitrogen (nitrates and ammonium), phosphates and silicates in the euphotic layer, analyzed by a multiple regression, showed that 70% of the PP variability was accounted for by the first three variables. While the significance of total Chl a was the highest, followed by phosphates, nitrogen had a negligible effect and that of silicates was not detected. In the surface layer (0–1m), the total phytoplankton biomass was co-dominated by dinoflagellates, the large cell diatom Pseudosolenia calcar-avis and the coccolithophore E. huxleyi. A weak bloom of E. huxleyi (cell abundance 1.0–1.8·106 cells L-1) was detected at 11 out of the 23 sampling stations. The relatively large thickness of the upper mixed layer (about 10m on average) and phosphorus deficiency were the main factors limiting the bloom of this coccolithophore.