The dissertation is devoted to the study of the composition, structure and spatiotemporal variability of the coastal fish assemblages for various natural and anthropogenic habitats of the North-Western Black Sea (NWBS). The species composition of off-shore fish assemblages off the coast of Odessa, Snake Island, in the Sukhyi and Hryhorivsky estuaries and near the Tarkhankut peninsula are studied for the first time using underwater observations, spearfishing. As well, the data of amateur angling and composition of fish thanatocenoses are taking into account for the first time.
The species composition of the coastal fish assemblages of the NWBS, which consists of 71 species, related to 34 families. Among them, 56 species found in the Gulf of Odessa, 43 in the Sukhyi Estuary, 41 in the Hryhorivskyi Estuary, 54 near the Tarkhankut and 41 near the Snake Island. Several fish species are recorded for the studied water bodies for the first time, i.e. Aidablennius sphynx, Parablennius zvonimiri, Planiliza haematocheila, Ophidion rochei, Coryphoblennius galerita, but in the Sukhyi Estuary also Lepomis gibbosus and Gobius bucchichi.
Long-term changes of coastal fish assemblages of the NWBS are registered. So, the increasing of the number of Hippocampus guttulatus, Pegusa lascaris and Chelon auratus in the Gulf of Odessa and adjacent waters are recorded since the end of 1990s. In 2000, Callionymus pusillus and Callionymus risso, which were not registered in the Gulf of Odessa in last 20 year, were found there.
The connection of the main coastal habitats of the North-Western Black Sea with the species composition, number and distribution of the coastal ichthyofauna has been revealed. The species composition and distribution of fish are influenced by 8 main natural and anthropogenic coastal habitats: sand, shells, pebbles, boulders, concrete blocks, coastal rocks, revetments and macrophytes.
The breakwaters, due to its similarity of their design with fyke-net, create obstacles for daily, seasonal and spawning migrations of fish. However, in the absence of a solid substrate, the presence of revetment structures in some cases creates the conditions for living, spawning and feeding of fish of the families Gobiidae, Syngnathidae and Blenniidae. The species composition and distribution of coastal fish fauna depends on the ratio of sand and rocky substrate. The largest species diversity has been recorded in the rocky habitats (57 species), and the highest number of fish has been observed in the boulders habitat (37 ± 5 ind.∙m-2). The average number of fish species in the sandy habitat areas ranges from 8 to 12 species depending of the area.
The influence of natural and anthropogenic factors of the NWBS ecosystem on the composition and abundance of coastal fish is estimated. The effect of hypoxia on the composition of the coastal fish assemblages is described as three stages:
1) Migration of Scopthtalmus maeoticus and Platichthys flesus individuals with their further concentration on up to 5-m depth; fish mortality not registered;
2) Concentration of S. maeoticus and P. flesus on the depth less than 3 m; appearance of cold-water fish; single dead individuals of different fish species;
3) Migration of the different fishes to the depth of less than 1 m, up to the water's edge; mass fish mortality is recorded.
It is established that the water area reflowing leads to reduction of species diversity by average of 25–30%. The largest reduction in the number of fish is observed for the families Gobiidae and Syngnathidae in 4 and 2 times, respectively.
The recommendations for the usage of behavioral responses of fish to assess the general level of anthropogenic pressure on coastal aquatic ecosystems are given. A system for assessment of the fish resistance to the fear factor on five-point scale has been developed. It is established that the behavioral responses of gobiid fish of age groups 2+ and 3+ can be used to determine the general level of anthropogenic load on coastal biocenoses.
The above data provide recommendations for maintaining species diversity, conservation of rare, endangered and endemic fish species, catch forecasts and, finally, more rational use of the Black Sea fish assemblages. These data are extremely important for the development of the Emerald Network, the definition of other protected areas, risk assessment for invasive species. Practical recommendations for the fish assemblages use to assess the anthropogenic load and quality management of marine coastal waters are also proposed.
