Large Luminous Plankton in Bioluminescence Peaks in the Black Sea

In the Black Sea, one peak was usually observed in the vertical profile of bioluminescence: in summer, this peak was recorded at a depth of 5–30 m at night and at a depth of 50–82 m in the daytime. Two peaks corresponding to the same horizons were detected in the morning, and in the evening at two of the fourteen studied stations. In the upper peak, a strong positive relationship was observed between the total intensity of bioluminescence and the abundance of the three dominant species: the correlation coefficient R was +0.79 for the plankton species Noctiluca scintillans and Oikopleura dioica , +0.70 for Oithona similis , and +0.82 for the total abundance of luminous plankton. In the upper peak, the abundance of these species showed a significant inverse dependence on temperature, while N. scintillans revealed a significant inverse relationship with changes in salinity ( R = −0.72). The dinoflagellate N. scintillans dominated in abundance at almost all stations. No significant correlation between bioluminescence and abundance of luminous species was found in lower peaks. We suppose that other zooplankton organisms also contribute to the bioluminescence field, whose ability to glow has not yet been studied.