Environmental control on macro- and mesozooplankton biomass off Sevastopol Bay: A 20-year analysis

Zooplankton constitute a key trophic link between primary producers and higher trophic levels in marine food webs, making them important indicators of environmental and climatic change. However, in many marine systems, long-term data are still limited, and major interannual fluctuations in zooplankton biomass and composition remain poorly understood. The article presents data assessing the impact of climate and warming in the Black Sea region on the interannual dynamics of macro- and mesozooplankton biomass in the outer shelf of Sevastopol Bay from 2002 to 2021. Over this period, the biomass of organic matter accumulated by gelatinous species has decreased, while that of mesozooplankton has increased by 15-20 %. Winter warming, which minimises convective mixing and nutrient transport into the zone of active photosynthesis, may have negatively affected the populations of the jellyfish Aurelia aurita, the dinoflagellate Noctiluca scintillans, and the chaetognath Parasagitta setosa. The increase in sea surface temperature (SST) during January-March appears to have a positive effect on microphages such as the copepod Paracalanus parvus and the appendicularian Oikopleura dioica. Early increases in SST during April-May, along with a synchronous improvement in the biogenic regime of the upper pelagic zone, suggest an increase in the biomass of large copepods (Calanus euxinus, Paracalanus elongatus, Acartia clausi and Centropages ponticus), regardless of their temperature tolerances. The extreme increase in SST during July-August was accompanied by the early development of ctenophores Beroe ovata and Mnemiopsis leidyi, as well as small crustaceans like Penilia avirostris and Oithona davisae. Overall, outer shelf macro- and mesozooplankton communities have remained relatively stable in species composition and total biomass of organic carbon. This study highlights the complex response of Black Sea macro- and mesozooplankton communities to regional warming, with species-specific seasonal sensitivities to changing environmental conditions.