Using the vertical sounding method for recording bioluminescence in the Antarctic sector of the Atlantic Ocean

Abstract

Bioluminescence is an essential element in the functioning of the pelagic community, which is associated with the key ecological role of light in the life of hydrobionts, inter alia in the formation of their spatial heterogeneity. The luminescence of marine hydrobionts is a manifestation of their vital activity in the form of electromagnetic radiation in the spectrum visible area, and its kinetic patterns are closely related to mechanism generating their chemical reactions and metabolic processes. Global warming, which undoubtedly has affected the Atlantic sector of Antarctica, caused serious structural and functional alterations in the pelagic community with repercussion on marine bioluminescence, an expressive indicator of environmental conditions. We aimed at studying the possibility of using the method of multiple vertical sounding by the hydrobiophysical complex “Salpa-M,” with simultaneous capture of biophysical and hydrological parameters at one station, to investigate the structure and length of fields of luminescence in Antarctic waters. The paper provides the technique for analyzing structural characteristics of bioluminescence, as well as material obtained during the 79^th Antarctic expedition onboard the RV “Akademik Mstislav Keldysh.” The core of the sounding method is raising (or lowering) the bathyphotometer “Salpa-M” at a constant speed in a given layer [usually, it is the upper productive (0–200 m) or the photic (0–100 m) layer] in the RV’s drift. Planktonic bioluminescent organisms, which are the main contributors to the formation of the bioluminescent potential of the pelagial, mostly illuminate when stimulated. Therefore, a bathyphotometer moving at a constant speed creates a standard level of the mechanical stimulation of bioluminescent organisms, and this allows to compare correctly the results of measurements for the vertical structure of the field of bioluminescence carried out in different areas and under various weather conditions (rolling, wind drift, etc.). The paper presents a fairly large data set of the integral bioluminescent signal at different horizons. Primary data on bioluminescence intensity, temperature values, electrical conductivity, and photosynthetically active radiation were obtained at 18 hydrographic stations in the studied water area of the Atlantic sector of Antarctica. The article considers an important issue related to the change in seawater bioluminescence in the Atlantic sector of Antarctica studied by the vertical sounding at different levels with a bioluminescent probe. When investigating bioluminescence, its vertical variability in the upper productive layer was determined in relation to features of plankton distribution. As a result, it was found out that the luminescence of Antarctic waters in the photic layer of this area occurs within the range from 8.4 × 10⁻¹² to 104.42 × 10⁻¹² W·cm⁻²·L⁻¹. Bioluminescence peaks (up to 104 × 10⁻¹² W·cm⁻²·L⁻¹) were recorded under the thermocline at a 45-m depth in the areas of concentration of the salp Salpa thompsoni Foxton, 1961 near the hydrological front, at a distance of about 6–7 miles on either its side. It is shown that the method of vertical sounding in Antarctic waters allows expressing the fields and the structure of aggregations of luminescent organisms.

Keywords: bioluminescence intensity, Atlantic sector of Antarctica, euphotic zone, vertical sounding, plankton