Abstract
Zooplankton plays an important role in aquatic food webs and changes in its abundance and diversity under changing climatic conditions can significantly affect the abundance and diversity of other aquatic organisms. The aim of the study was to assess quantitative and qualitative parameters of zooplankton development, dynamics of development of its dominant groups and the effect of water temperature. Species composition and abundance of zooplankton of the Kremenchuk Reservoir were studied in 2006, 2010–2012 and 2020 in relation to water temperature and pollution. Zooplankton species diversity fluctuated significantly over the years of the study. A total of 46 taxa were recorded in the reservoir during the study period. The number of recorded zooplankton taxa ranged 26 to 32 depending on the year. The most abundant zooplankters were Chydorus sphaericus, Copepoda nauplii, Brachionus diversicornis. The abundance of zooplankters in the reservoir during the study period ranged 23·103 to 256·103 ind./m3, and biomass 0.14 to 0.89 g/m3. A significant positive relationship was observed between the abundance of cladocerans, including some individual species (Ch. sphaericus and Ceriodaphnia sp.), and water temperature. Indicator species of water pollution in different years and in different parts of the Kremenchuk Reservoir differed significantly, which probably depended on the presence or absence (in a certain period of time) of polluting discharges. The total saprobity index in different years in different parts of the reservoir was in the range of 1.5–1.9. Structural indicators of zooplankton and its dominant complexes characterize the water in the Kremenchuk Reservoir as β-mesosaprobic. It is probably too early to assess the impact of climate change zooplankton as these changes are still unstable and short in time, but it is necessary to constantly monitor the biota of aquatic ecosystems to further study and summarize the data, which could later allow an identification of such changes.
Highlights
The Dnipro reservoirs are a unique man-made objects, the ecological state of which develops under the impact of a complex of factors of external and internal origin
The least pronounced year-to-year fluctuations were recorded for copepods (CV was 38.9% for the abundance and 64.4% for biomass)
No significant trends were detected between the abundances and biomasses of copepods and rotifers and water temperature during the study period (Fig. 1 and 2)
Summary
The Dnipro reservoirs are a unique man-made objects, the ecological state of which develops under the impact of a complex of factors of external and internal origin. Changes in zooplankton abundances in response to rising average temperatures were shown for some reservoirs and lakes (Jeziorski et al, 2016; Korneva et al, 2019); in other lentic systems, the dynamics of zooplankton abundances in the context of climate change did not show clear trends (Carter & Schindler, 2012; Fomina & Syarki, 2018) In this regard, there is a question about the impact of these changes on the structural and functional parameters of main groups of aquatic organisms as a component of the study of patterns of transformation of aquatic ecosystems in conditions of regulated river flow and multi-vector impact of external factors (Romanenko et al, 2019)
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