The Spatial Variability of the Fluorescent Characteristics of Phytoplankton in the Black Sea

Abstract

The spatial variability of the photochemical efficiency of phytoplankton photosystem II was analyzed in two contrasting regions of the Black Sea: the western part of the deepwater region and a region influenced by the Danube River discharge. The fluorescence values for open (F₀) and closed (F_m) photosystem II reaction centers in the investigated areas varied by an order of magnitude and correlated closely. The potential photochemical efficiency of phytoplankton photosystem II (F_m − F₀)/F_m varied from 0.16 to 0.70. Three types of the vertical distribution of this index were found. In the first type, the values increased from the surface to the top of the thermocline and then remained stable down to the bottom of the euphotic zone; in the second type, they increased from the surface to the bottom of the euphotic zone; in shallow areas, they were stable within the euphotic zone. With an increase in light intensity, the phytoplankton photochemical efficiency decreased. The light inhibition of the photosystem II efficiency was more intense in the deeper than in the upper layers of the euphotic zone.