The findings of the study on the impact of hypoxia on the glow of the Black Sea ctenophore Mnemiopsis leidyi A. Agassiz, 1865 of three size groups (20-30, 30-45, and 45-60 mm) were obtained under experimental conditions. Peculiarities of ctenophore bioluminescence were studied during mechanical and chemical stimulation under the conditions of normoxia (at an oxygen concentration of 5.6-6.7 mg O 2 L À1 ), moderate hypoxia (2.5-2.8 mg O 2 L À1 ), and acute hypoxia (1.2-1.5 mg O 2 L À1 ). An increase in the amplitude and energy of luminescence of the ctenophores mechanically and chemically stimulated was observed at an oxygen concentration of 1.2-1.5 mg O 2 L À1 (acute hypoxia) in two size groups in the lobate form (30-45 and 45-60 mm). The inhibition of amplitude, energy, and duration of the signal was regis-

The work presents the findings of the laboratory and in situ studies of ctenophore Pleurobrachia pileus O.F. Müller, 1776 which have shown that this species has bioluminescent properties. These organisms were considered non‐luminous before. P. pileus bioluminescence was studied on board RV Professor Vodyanitsky during its 116th voyage. Sampling live organisms was preceded by probing with the Salpa MA+ probe to register the daily maximum glow in redoxcline, which in this zone was recorded, as a rule, in the depth range of 60–70 m, where dense clusters of P. pileus were formed at that time. The samples of ctenophores were taken by a Bogorov–Rass plankton net. After the net was closed, it was lifted to the surface at a speed of 0.4–0.5 m s−1. It was shown that only at a temperature not exceeding 14°C, the P. pileus remained alive for 2–3 days. The data provided indicate that the temperature above 14°C is close to the maximum permissible for P. pileus; therefore, chemical and mechanical stimulation experiments were carried out at this temperature (14°C) to agitate ctenophores luminescence. Though, the nature of their signal was significantly different. The total percentage of luminous organisms from the entire catch was 32.43%, which unequivocally proves that P. pileus glows and makes a significant contribution to the intensity of the glow at great depths in redoxcline.

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.

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