THE ECOLOGY OF THE CALANUS-PONTICUS POPULATION IN THE DEEPER LAYER OF ITS CONCENTRATION IN THE BLACK-SEA

The layer of daytime concentration of Calanus ponticus (VC and VI C) performing daily vertical migrations and the layer of 'winter stock' aggregation are confined to the depth of maximal gradient of the main pycnocline under an unusually sharp oxycline. The concentration layer thickness ranges from 2 to 20-30 m and the Calanus concentration in it is > 250 ind. m-3, sometimes being 3500 ind. m-3 and even more. The population in the concentration layer is divided into two ecological groups: I, feeding and migrating specimens of copepodite stages V and VI, their body lipid contents being 25-60-mu-g min.-1; and II, non-feeding and non-migrating specimens of copepodite stage V, their body lipid contents being 100-150-mu-g ind.-1. The relationship with oxygen concentration was studied in both ecogroups. The experiments show that specimens of ecogroup II can exit at an oxygen concentration of 0.06 ml l-1, but at such concentration falling into anabiosis. They die at 0.04 ml O2 l-1. Estimates of respiration of the group II specimens ('winter stock') show that lipids they store are sufficient for 7 months' survival. Depth of Calanus concentration is determined by water density rather than concentration of oxygen.