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 O 2 ·L -1 ), moderate hypoxia (2.5-2.8 mg O 2 ·L -1 ), and acute hypoxia (1.2-1.5 mg O 2 ·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 O 2 ·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, that is the process during which photons are emitted. The response of the bioluminescent system to a decrease in О 2 concentration can be associated with an increase in the production of ROS that provides high values of the ctenophore luminescence under hypoxic conditions.