Ichthyofauna of the Black Sea coastal zone in the Laspi Bay area (Crimea)

The ongoing processes of the Black Sea salinization and fluctuations in mean annual temperature have already caused the natural dispersal of various representatives of the Mediterranean Basin and Indian Ocean fauna and led to a change in species composition and structure of fish communities, inhabiting the coastal zone of the Crimean Peninsula. As a result, it became necessary to study modern composition of fish fauna and indicators of its species richness and diversity. The Laspi Bay was chosen as a model polygon for the following reasons: relatively low level of anthropogenic load; the fact that its part belongs to the specially protected natural areas, as well as the absence of fishing activity with coastal fixed fishing gear; constant free entry of pelagic fish species; biotopes diversity; and smooth change in depth. These peculiarities of the Laspi Bay allow assessing the presence of fish from different ecological groups and provide conditions for monitoring. The study was carried out in the spring-autumn periods of 1990–1994 and 2017–2018. The material was sampled with net fishing gear, hook tackle, and traps. The nets were set at various depths both perpendicular and parallel to the shoreline during the day (10:00 to 18:00) and at nighttime (18:00 to 06:00). Visual observations were also carried out. In total, 70 fish species were registered. Out of them, 14 species were previously not recorded for this area; 5 of them [salema Sarpa salpa (Linnaeus, 1758), red-mouthed goby Gobius cruentatus Gmelin, 1789, Bath’s goby Pomatoschistus bathi Miller, 1982, mystery blenny Parablennius incognitus (Bath, 1968), and chestnut goby Chromogobius quadrivittatus (Steindachner, 1863)] are recent invaders, actively spreading in the Black Sea over the past 15–20 years only. Most of the analyzed species (64) are marine euryhaline fish. The brackish-water group is represented by three species, indigenous to the Black Sea: mushroom goby Ponticola eurycephalus (Kessler, 1874), round goby Neogobius melanostomus (Pallas, 1814), and knout goby Mesogobius batrachocephalus (Pallas, 1814). Out of anadromous fish, starry sturgeon Acipenser stellatus Pallas, 1771 is registered, as well as two Clupeidae species: Black Sea shad Alosa tanaica (Grimm, 1901) and Pontic shad Alosa immaculata Bennett, 1835. As established, the observed seasonal dynamics of species diversity indices within the studied water area is associated with fluctuations in the abundance of horse mackerel Trachurus mediterraneus (Steindachner, 1868). In April – May, when this species headed to shallow water for feeding and breeding, the indices have the lowest values; in August, when the abundance of horse mackerel decreases, the maximum values are observed.