The dissertation is devoted to the study of the diversity, structure and influence of the main ecological factors on the distribution of harpacticoid copepods in the composition of meiobenthos for different contact zones of the north-western part of the Black Sea (NWBS). The species composition and peculiarities of the formation of groups of harpacticoid copepods on four contour biotopes of NWBS were studied. In the faunal analysis of harpacticoid copepods of contour biotopes, for the first time for the Ukrainian part of the NWBS the list of species was expanded from 116 to 127. A new species for the fauna of the Ukrainian sector of the NWBS was noted. The following species complexes of harpacticoid copepods are formed in NWBS: lithocontour of macrophytes and mussel fouling on natural hard surfaces and a complex of mollusks with algae of artificial surfaces of Odessa marine region (OMR), lithocontour of Snake Island, interstitial fauna, psammocontour of sublittoral, pelocontour of OMR and Yahorlytska and Tendrovska bays, coastal and deep-water fauna of potamocontour. The groupings of harpacticoid copepods of pseudolitorals differ from supralitorals by richer species diversity and are characterized by the presence of specific interstitial species Arenopontia subterranea, Paraleptastacus ponticus and Vermicaris pontica. The horizontal distribution has a clear zonation: the number and biomass increase in the horizon 0–10 cm at the water’s edge (from 1268–2890 ind. ‧ 100 cm-3 and 20.29–46.43 mg ‧ 100 cm-3, respectively), and then there is a sharp decline in these indicators on the horizons of depths of 20-60 cm, where the maximum values do not exceed 500 ind. ‧ 100 cm-3, and biomass 8 mg ‧ 100 cm-3. Species complexes of harpacticoids of the upper sublittoral of the psamocontour consist mainly of epibenthos species. The largest number of harpacticoid copepods is observed at a depth of 0–4 m, and then decreases with increasing depth (R2 = 0.9848). At stations far from shore, it was possible to trace the dependence of the number of harpacticoids on the oxygen saturation in the bottom layer of water (the coefficient of determination is R2 = 0.7463). On the grouping of harpacticoid copepods of the lithocontour of OMR and Snake Island is affected by the character of the substrate. On natural hard surfaces with fouling of algae U. intestinalis a high diversity of species was observed, with the lowest quantitative indicators of harpacticoid copepods (indicators of average number did not exceed 4000 ± 577 ind. ‧ m-2, and biomass 64 ± 9.2 mg ‧ m-2). The periphytals of artificial pools are characterized by less species diversity, and the contribution of harpacticoids to the number and biomass on traverses in most cases does not exceed 10%. In the study of harpacticoid copepods of the OMP pelocontour, three times more species were found on gray mules than on black ones. At depths of 5 to 15 m, high numbers of harpacticoids are observed (average value 62,568 specimens ‧ m-2), and their contribution to total meiobenthos averages 21.65%. In areas of pelocontour OMR with low oxygen concentration, unfavorable for harpacticoid copepods are formed, while the number of anaerobic species of nematodes increases (the coefficient of determination of the degree dependence of nematode-harpacticoid index on oxygen concentration is 0.8574). In the potamocontour, the species complex of harpacticoid copepods of the coastal part is richer in comparison with deep-water areas. The main factor in the distribution of the number and biomass of harpacticoid copepods of the potamocontour is the degree of distance from the mouth of the river. The obtained results of work on the species diversity of harpacticides can be used in environmental practice to assess the state of biodiversity in NWBS. Information on the number of harpacticoid copepods in comparison with the number of nematodes can serve as a reliable tool for monitoring the state of the environment of the Black Sea-Mediterranean basin on loose soils. Studies of the distribution of biomass and the number of harpacticoid copepods and their contribution to total meiobenthos depending on environmental factors in the contour biotopes of NWBS will be useful in assessing the forage base of ichthyofauna of the region. Data on the peculiarities of the functioning of harpacticoid copepods in the meiobenthos of contour biotopes can be used in pedagogical practice in the preparation of textbooks for practical and lecture classes on biodiversity of benthic fauna for students majoring in "biology", "zoology", "ecology", "hydrobiology".
