Impact of hypoxia conditions on the Mnemiopsis leidyi A. Agassiz, 1865 bioluminescence.

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 O2  L-1 ), moderate hypoxia (2.5-2.8 mg O2  L-1 ), and acute hypoxia (1.2-1.5 mg O2  L-1 ). 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 O2  L-1 (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 registered in M. leidyi ctenophores at the transitional stage from larva to the lobate form under conditions of acute hypoxia. It was noted that in normoxia, the values of the amplitude and energy of the bioluminescent signal of M. leidyi increase along with a size growth of an individual. This phenomenon was observed both during mechanical and chemical stimulations. Under conditions of acute hypoxia, this trend was mainly preserved. The universality of the relation between the bioluminescence of the organisms and their bioenergetics is obvious. The bioluminescent system of ctenophores has the role of an antioxidant system and is engaged in the neutralization of reactive oxygen species (ROS), that is the process during which photons are emitted. The response of the bioluminescent system to a decrease in oxygen concentration can be associated with an increase in the production of ROS that provides high values of the ctenophore luminescence under hypoxic conditions.

Research into bioluminescence of the Black Sea ctenophores Pleurobrachia pileus O.F. Müller, 1776.

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.

Field studies of bioluminescence in Bransfield Strait in 2022.

In January 2022, during scientific cruise 87 on the RV Academic Mstislav Keldysh in the Atlantic sector of the Southern Ocean, three hydrobiophysical cross-sections were performed in the Bransfield Strait. Bioluminescent signals were measured in a layer of 0-200 m at each of the 24 stations located at three sites. For the first time, a new hydrobiological system 'Salpa MA +' was used, which made it possible to obtain novel data in the photic layer of the studied water area. Bioluminescence studies were accompanied by simultaneous measurements of background indicators: temperature, electrical conductivity, photosynthetically active radiation, and they were compared with the data from plankton samples processing. Bioluminescent potential was registered at almost all the stations. The maximum level of bioluminescence was registered in the area of the archipelago of the South Shetland Islands, where the maximum accumulation of Salpa thompsoni, Foxton 1861 was noted. The purpose of this work is to identify the main factors and patterns affecting the intensity of the bioluminescence field in the region under study.

Field studies of bioluminescence in the Antarctic sector of the Atlantic Ocean in 2002 and 2020.

In this work, IBSS materials on seawater bioluminescence intensity changes in the Atlantic sector of the Antarctic Ocean (the Weddell Sea area) with an interval of almost 20 years are presented. Data were obtained using a single instrument, the hydrobiophysical system Salpa-M, in the area of 50-63°S, 62-49°W in March 2002 (183 soundings at 45 stations during cruise 7 on RV Gorizont) and in February 2020 (122 soundings at 18 stations during cruise 79 on RV Academic Mstislav Keldysh). The bioluminescence studies were coupled with the simultaneous measurement of temperature, electrical conductivity, and photosynthetically active radiation, and they were compared with the data from processing plankton samples. Over the past 20 years, as a consequence of the appearance of a large number of gelatinous organisms and the resulting changes in the structure of the plankton community, the bioluminescence of Antarctic waters in the euphotic layer of this region has decreased almost two-fold, currently being in the range 8.4 × 10-12 to 104.42 × 10-12  W·cm-2 ·L-1 .

Bioluminescence of ctenophores near the boundary of oxygen-depleted waters at the redoxcline of the Black Sea.

Vertical distribution of ctenophores near the boundary of oxygen-depleted waters of the Black Sea redoxcline was studied by use of video observations with real-time water sampling, horizontal MultiNet towing, and soundings using bathyphotometers with simultaneous vertical plankton net sampling. The results of the study showed for the first time that the daytime accumulation of ctenophores above the upper boundary of the suboxic zone changes the biophysical properties of the medium, causing an increase in the daytime intensity of bioluminescence near the redoxcline. The dynamics of this glow is in antiphase to that in the surface layers, where it is associated with the bioluminescence of phytoplankton. Therefore, in the deep-sea areas, two types of bioluminescence peaks differ in the light generation sources: the nighttime glow of phytoplankton in surface layers and the daytime glow of zooplankton in layers of oxygen-depleted waters at the redoxcline. The discovery of this new phenomenon allows the use of bioluminescent methods for the rapid assessment of the depth of the daytime zooplankton layers for the subsequent hauls of plankton nets. This significantly expands the possibilities of studying the structure and functioning of the pelagic ecosystem of the Black Sea and other marine basins with a redoxcline.

Ecological role of bioluminescence of Black sea ctenophores.

Bioluminescence, which is a manifestation of the vital activity of an organism in the form of electromagnetic radiation in the visible area of the spectrum, is a highly important ecological and optical factor of the marine environment. Until recently, it was believed that microplankton - bacteria and dinoflagellates - exceptionally contribute to the formation of the bioluminescence field in the Black Sea, as well as in other regions of the World Ocean. However, the ctenophores Mnemiopsis leidyi A. Agassiz, 1865, and Beroe ovata Mayer, 1912, which invaded the Black Sea in the 1980s-1990s, are also luminous organisms whose bioluminescence intensity is millions of times greater than that of most microplankton representatives. It is known that the characteristics of bioluminescence can reveal the state of the organism and, consequently, the state of the environment. At present, there is a fairly large number of works devoted to the physiology and ecology of the Black Sea ctenophores. In recent studies, the variability of light emission parameters of ctenophores following their functional state was revealed. Intensity and duration of light emission as parameters of the ctenophore bioluminescent signal as well as the influence of various abiotic and anthropogenic environmental factors on the ctenophore luminescence have been studied. However, the significance of bioluminescence for the living activity of ctenophores remains unclear. In connection with the above, it is extremely important to assess the ecological role of the bioluminescence of the Black Sea ctenophores.