Spatial distribution of ichthyoplankton near the Crimean Peninsula in the summer spawning season 2013

Abstract

Data obtained in five complex cruises of RV “Professor Vodyanitsky”, carried out from May to September 2013, in the summer spawning season, are analyzed. The dynamics of ichthyoplankton species diversity and spatial distribution depending on hydrological regime peculiarities in different regions of the shelf and open waters of the Black Sea off the Crimean Peninsula is presented. Totally 17 species of fish eggs and larvae from 13 families were identified in ichthyoplankton, maximum number of species was observed in June. Average eggs and larvae numbers during the spawning season were 50.5 and 9.2 specimen per m², respectively. Maximum abundance of eggs and larvae was observed in July (109.9 and 9.2 specimen per m², respectively). Eggs and larvae of anchovy Engraulis encrasicolus (Linnaeus, 1758) dominated: their proportion in open waters in the height of the spawning season amounted 96 and 94 %, respectively. Maximum indexes of species diversity and evenness (significance of each species) were observed in May, at the beginning of spawning season, when dominant species had just started their spawning and their abundance in ichthyoplankton was comparatively low. Species richness indexes reached the maximum value in June, when maximum species number in ichthyoplankton was observed. Species composition and spatial distribution of ichthyoplankton depended on the thermohydrodynamic structure of the sea in the studied regions, and decline of jelly plankton pressing on ichthyoplankton fodder base contributed to the survival of fish larvae. The most significant factors determining the thermohydrodynamic structure of the sea in the summer spawning season 2013 were: regional peculiarities of the sea surface warming up regime in spring-summer period and its cooling in autumn hydrological season; advective contribution of surface currents (first of all, the Main Black Sea Current); wind-driven processes (upwelling and vortex dipole) in the coastal regions; local thermohaline inhomogeneities in the areas of freshened river water mixing with shelf waters in the north-western part of the Black Sea and the Sea of Azov waters at the beginning of the Kerch Strait mixing with open sea waters.