Small-scale plankton patchiness in the Black Sea euphotic layer

Abstract

Small-scale horizontal heterogeneites or patches of bioluminescence intensity and sound volume back scattering strength (SVBS) were studied in the central part of the Black Sea in October, 1989. Bathyphotometric casts and measurements of SVBS, were taken every 3 minutes in the surface layer (0–20 m) over a period of several hours from a drifting vessel. Casts were accompanied by temperature profiles and zooplankton sampling. Measurements were carried out during the day and night periods. From adaptive spectral analysis it was shown that the horizontal dimensions of the bioluminescent and SVBS heterogeneities were between 75 to 1500 m and 20 to 443 m respectively. In the case of zooplankton biomass the dimensions were 85 to 818 m and 80 to 1800 m for the temperature field. Physical and dynamical factors dominate in the formation of small-scale spatial heterogeneity of the studied fields. Biological factors, such as diel vertical migrations, trophic interactions etc. will also contribute to the formation of patches at night.