Quantitative Distribution and Lipid Reserves of the Calanus euxinus (Copepoda) Population in the Black Sea in Late Autumn 2017

Abstract—

The field data on the abundance, biomass, age structure, and lipid reserves of the copepod Сalanus euxinus population in deep pelagial and Crimean shelf regions of the Black Sea in November 2017 were analyzed. The abundance and biomass of this species in deep areas (10.2 ± 0.5 × 10³ ind./m² and 7.3 ± 0.5 g/m², respectively) were similar to the average annual values for seasons with moderate development of planktivorous jellyfish populations. The average abundance and biomass of the copepods were similar to analogous 2016 values when the jellyfish abundance was twice as low. However, in 2017, the denser aggregations of C. euxinus (12.8 ± 1.0 × 10³ ind./m² and 9.8 ± 0.5 g/m²) were found in the central parts of cyclonic circulations, while in 2016, they were recorded more frequently at the peripheries of cyclonic gyres. A structure of the C. euxinus population also changed. In November 2017, the percentage of copepodites I–IV, females and males, increased, whereas the proportion of copepodites V reduced. These changes likely resulted from a later sampling period in 2017, when the C. euxinus population was ready for active reproduction. Sufficient amounts of lipids in copepodites V, decreased oil sac volumes in females, and increased abundance of males in anticyclonic regions are indicative of more favorable trophic conditions for this part of the C. euxinus population and its higher maturity.