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

Abstract

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.

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

“…According to our previous studies, the luminescence of the Black Sea ctenophore Pleurobrachia pileus (O.F. Müller, 1776) in the suboxide zone was established [24], which, combined with a surge in ROS production during histotoxic hypoxia [18], makes it suggest a luminescence mechanism involving ROS with low PO 2 values.…”

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

“…Ctenophores spend the night in the upper water layers, usually just below the thermocline, descending to the depth of 80 to 150 m in early morning and ascending again in the late afternoon [2, 14]. The mentioned migrations were observed in our expeditions [21]. These migrations do not occur in winter, when P. pileus remains close to the bottom, often ceasing movement of the cilia combs.…”

“…It was established that bioluminescence at redoxcline has a daily rhythm associated with ctenophore migrations: during the day it increases when they smoothly migrate to the lower boundary of the oxygen zone, and at night this glow disappears. The dynamics of ctenophore bioluminescence at redoxcline is in antiphase to that in the surface layers, where it is associated with phytoplankton bioluminescence [21].…”

“…However, in several experiments in the autumn-winter and spring periods, P. pileus was luminous when stimulated both mechanically and chemically (Figure 5). The seasonal variability of the glow of this species can be explained both by seasonal fluctuations in the water temperature in the Black Sea and by the peculiarities of its ecology: small individuals concentrate in the upper part of the thermocline, while the larger ones are found near the redoxcline with an oxygen concentration of slightly more than 1 ml L À1 [20,21,24]. It has been shown that adult pleurobrachias prefer to live under the thermocline up to the lower boundary of the oxygen zone [21].…”