Dynamics of abundance and biomass of pontogammarus (Pontogammarus maeoticus Sowinsky, 1894) in the eastern Azov Sea in the context of changing water salinity in 2001–2023
Authors:   Russian Federal Research Institute of Fisheries and Oceanography (FSBSI “VNIRO”), Azov-Black Sea Branch of the FSBSI “VNIRO” (“AzNIIRKH”), Saenko E. M. , Kotov S. V. ,   Russian Federal Research Institute of Fisheries and Oceanography (FSBSI “VNIRO”), Azov-Black Sea Branch of the FSBSI “VNIRO” (“AzNIIRKH”)
Published: December 2024

Background. The ongoing climatic changes have a significant impact on the fishing resources of the Azov Sea. Relevance. Due to the depressed state of the stocks of traditional fishing targets, it is urgent to search for alternative ones that can compensate for the shrinking catches and ensure the development of fishing in new environmental conditions. The aim of this work was to assess the abundance and biomass dynamics of the pontogammarus in the context of the increasing salinity. Methods. This work is based on the data collected over the course of the 2001–2023 studies on the assessment of the abundance and biomass of the pontogammarus population in the Azov Sea, taking into account the habitat parameters (namely, salinity). The pontogammarus samples were collected in the supralittoral zone with a benthic frame and a sampling trap, and in the upper sublittoral zone at a depth of 0.5 m with a trap. The samples were fixed with 4 % aqueous formaldehyde solution. The laboratory processing included the determination of the species, sex, dimensional characteristics, the number of individuals in the sample, and the individual weight of the crustaceans. Results. In 2001–2015, within the salinity range of 9.64–13.24 ‰, an increase in the specific abundance and biomass of the population was recorded in the Azov Sea. A significant positive relationship was found between the specific abundance, specific biomass and salinity of the sea (r=0.87–0.91). A further increase in the salinity to 14.91–15.29 ‰ in 2021–2023 had an adverse effect on the density of crustacean distribution as compared to that in 2015. Correlation analysis revealed a strong negative relationship (r=-0.99) between the salinity and the number of crustaceans in the aggregations, as well as their biomass. In Taganrog Bay, at a salinity of 5.26–7.34 ‰, the abundance and biomass had the lowest values compared to the entire area of the Azov Sea. With the increase in the salinity in 2009–2015, there was also recorded an increase in the specific abundance and biomass of the pontogammarus. A strong positive relationship (r=0.90–0.92) was identified between quantitative indicators of population distribution and water salinity. In subsequent years (2021–2023), the relationship between the quantitative characteristics of the pontogammarus population and the salinity in the bay remained positive. Conclusion. The water salinity in the range of 11.25–13.24 ‰ is optimal for the vital activity of pontogammarus; it is the level at which the aggregations with the highest abundance and biomass can be formed. If the water salinity of the Azov Sea continues to increase, in the following years, a decrease in the abundance and biomass of crustacean aggregations is expected, which will lead to the reduction in the total stock of this exploitable resource.