Role of abiotic and biotic factors in formation of the seasonal variability of bioluminescence fields in the Sea of Azov

Abstract

More than 150 intensity profiles of the bioluminescence field at 4 hydrographic stations were obtained for the first time in the Sea of Azov. The profiles were performed with a discreteness of 1 m in depth, as well as temperature and electrical conductivity profiles; microplankton species composition was also analyzed. Measurements of vertical profiles of the photosynthetically active radiation were also made during daytime. Almost at all the stations, along with the bioluminescence field measurements, samples of microplankton were taken by Jedi nets and bathometers for subsequent analysis of its species composition and quantitative distribution. Studies were carried out in winter, spring and summer periods on a unified grid of stations. The pronounced seasonal variability of the bioluminescence field integral values and its vertical structure at the Sea of Azov was registered, that was determined by the superposition of biological and hydrological characteristics of the water column in the study areas. The minimum values of the bioluminescence field intensity at the Sea of Azov (6.05 × 10-12 W·cm-2·l-1 at a depth of 4 m) were recorded in winter period. It was mainly due to low water temperature of 0.5–1.5 °C in the late January and early February, that resulted in low abundance of luminous plankton. With spring warming up of water (at water temperature 12.5 °C) the development of the unicellular plankton intensified and an increase of the bioluminescence intensity in the bottom layer to 34.8 × 10-12 W·cm-2·l-1 was observed. In the summer period, maximum values of the bioluminescence intensity were registered (up to 634.4 × 10-12 W·cm-2·l-1) at average water temperature of 27.5 °C and at maximum abundance and biomass of the luminous phytoplankton fraction.

Keywords

• pelagial
• euphotic layer
• phytoplankton
• bioluminescence
• vertical structure