The A.O. Kovalevsky Institute of Marine Biological Research of RAS, Sevastopol, Nachimov av., 2
Based on studies carried out in the Black Sea in May 2013, the main factors controlling the spring bloom of the coccolithophorid Emiliania huxleyi were identified. This algae plays an important role in the formation of carbon and sulfur cycles in the World Ocean, and also affects the optical and thermal characteristics of surface waters during its intensive development.
The purpose of this work was to identify the role of the abiotic and biotic factors in the formation of the spring E. huxleyi bloom in the Black Sea.
Experimental studies were carried out in the coastal and open waters of the Black Sea during the 72nd scientific expedition on the R/V “Professor Vodyanitsky” (May 20-29, 2013). Works were carried out both in the western part of the sea (up to 34 ° E) and in the east part (34 – 37º E), in the surface layer (0-1 m). A complex of structural and functional parameters of phytoplankton, as well as abiotic environmental conditions was determined.
Studies have shown that the development of E. huxleyi bloom in the Black Sea begins in May. This phenomenon was controlled by the joint influence of several abiotic factors such as light, temperature and nutrients, as well as the biotic factor – microzooplankton grazing. In the work period, favorable light and temperature conditions were observed for the growth of phytoplankton. The average temperature of the water in the upper mixing layer was about 20 °C, and the intensity of the solar radiation was here on average 24 E·m-2·day-1. The main source of nitrogen was ammonium, which was favorable for the development of E. huxleyi, as well as dinoflagellates. Under optimal abiotic conditions, E. huxleyi grew with a maximum rate for this species (1,00-1,40 day-1). However, nitrate deficiency limited the growth of diatoms.
The weak consumption of E. huxleyi by microzooplankton has contributed to an increase in the abundance of its cells. The growth of dinoflagellates was limited by their significant consumption by microzooplankton. This group of algae was probably the main source of food for Protozoa during the research period.
Thus, conditions favorable for light, temperature and nutrients for growth of E. huxleyi, as well as its low consumption by microzooplankton, contributed to an increase in the proportion of this species of algae in phytoplankton. The main abundance and biomass of phytoplankton was, as a rule, in this small coccolithophorid. All its cells were covered with coccoliths – plates of calcium carbonate. The cell diameter was 5-6 µm, and the abundance was 1,6-4,3 millions cells· l-1.
Keywords: phytoplankton, coccolithophorid Emiliania huxleyi, the Black Sea.
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