Peculiarities of seasonal dynamics of net primary production and its microzooplankton grazing in the coastal waters of the Black Sea (Sevastopol region)

Abstract

The studies of net primary production (NPP) seasonal dynamics, its microzooplankton grazing were conducted at two stations in the western Black Sea coastal waters near Sevastopol during a period from January 2020 to December 2022. Each year, one maximum of the phytoplankton NPP (280–820 mg C·m-3·day-1) was observed in July, when the water temperature ranged from 22 to 25 °C, and solar radiation intensity was 48–50 E·m-2·day-1. Large diatoms and dinoflagellates played a key role in its formation. At this time, the values of the net phytoplankton growth rate were 0.3–1.0 day-1, and the relative share of primary production consumed by microzooplankton (g/m) did not exceed 26%. In December – February, when the water temperature was 8.0–13.5 °C and the intensity of solar radiation was 10–15 E·m-2·day-1, the NPP decreased to a minimum (4–38 mg C·m-3·day-1). Under these conditions, the net phytoplankton growth rate decreased to 0–0.40 day-1, and g/m was 15–100%. For three years at station 2, the contribution of large algae with cell volumes from 4000 to 18000 µm3 in the NPP was significantly higher than at station 1. It was 61.1 % in 2020, 69.7 % in 2021 and 23% in 2022. The consumed NPP for this size group of algae was 54 % in 2020, 68.4 % in 2021 and 47.8 % in 2022.