Aisylu G. Ibragimova

Cladocera are an important component of freshwater zooplankton and serve as proxies in paleoecological reconstructions. However, the similarity of environmental signals reflected in the dominant species structure of contemporary (CC) and subfossil (SC) cladoceran communities remains an open question. The objective of this study is to assess how changes in the dominant species structure of SC correlate with those in CC and with corresponding environmental conditions in artificial ponds. The research was conducted in seven artificial urban ponds in Moscow experiencing various degrees of anthropogenic pressure. Samples of both CC and SC were collected simultaneously from the same locations along a depth gradient: from the littoral zone, through intermediate depths, to the deepest part of each pond. During sampling, the following parameters were measured: depth (DEPTH), temperature, dissolved oxygen concentration, pH, conductivity (COND), oxidation‐reduction potential, blue‐green algae phycoerythrin, blue‐green algae phycocyanin, and chlorophyll a. In total, 22 CC and 26 SC samples were collected; 23 species were identified in the CC samples and 38 species were identified in the SC samples. Although the SC samples contained a greater number of species, several significant taxa from the CC samples were either rarely detected or completely absent from the SC samples. Redundancy analysis (RDA) and k‐means clustering revealed five clusters for CC and four for SC, which were distributed along gradients of Depth and COND. Further analysis revealed synchronous changes in species structure in both CC and SC communities along the COND and DEPTH, which aligns with the established ecological preferences of the taxa. That suggest the structure of CC and SC communities in artificial water bodies—even of small size—mirrors specific patterns, resulting the formation of distinct species assemblages. Shifts in dominant species structure within CC and SC may be useful for reconstructing DEPTH, while COND can only be roughly estimated based on the presence of certain subdominant species. The study also discusses the implications of cladoceran species preservation for reconstructing environmental variables.

Remains of Rhynchotalona latens (Sarmaja-Korjonen, Hakojärvi et Korhola 2000) were found in the bottom sediments of several glaciogenic lakes in northwestern Russia. Subfossil remains of the species were noted both in the bottom sediments of the Late Pleistocene and Mid-Holocene. We discovered a rare species, R. latens, in the bottom sediments of Lake Medvedevskoye (Karelian Isthmus). This species prefers shallow oligo-mesotrophic lakes with organic sediments and has attracted the interest of scientists around the world as it is considered a glacial relict and has recently been found in surface sediments and as a living population in Finland and Russia.

The analysis of loss on ignition (LOI) is widely used in paleolimnological reconstructions to understand the conditions of sedimentation and to identify the input of organic matter from external sources as well as pollution in lakes. For the first time in Russia, the influence of organic matter content on Cladocera distribution in five columns of lake bottom sediments in the Kola-Karelian region was analyzed. Using linear regression in the PAST program, it was found that Biapertura affinis, Alona quadrangularis and Camptocercus rectirostris increase in abundance with rising organic matter content, whereas Chydorus cf. sphaericus <and Bosmina (Eubosmina) cf. longispina thrive in conditions of low organic matter content.

Over the last decades significant progress was achieved in the investigations of water fleas (Crustacea: Cladocera). Their morphology, taxonomy and biogeography can be considered as well-studied, but still there are genera almost ignored by taxonomists. The genus Ceriodaphnia Dana, 1853 (Cladocera: Daphniidae) belongs to such problematic groups. From previous publications, it is obvious that different taxa from the genus have a very different morphology of their ephippia. Here, we study ephippium morphology in six common taxa from central-northern European Russia (Ceriodaphnia megops Sars, 1862; C. laticaudata P.E. Willer, 1867; C. rotunda (Straus, 1820) sensu Sars, 1862; C. quadrangula (O.F. Muller, 1785); C. puichella Sars, 1862; C. reticulata (Jurine, 1820)) using light and scanning electron microscopy. A key to their identification based on ephippium morphology is proposed. This could be the starting point for revisions based on morphological characters with special emphasis on ephippia. Also, we propose that Ceriodaphnia taxa at least from the Holocene subfossil samples could be identified to the species group level according to structure of their ephippia. This approach to identification of Ceriodaphnia remains in sediments could improve palaeoecological reconstructions. However a global revision of the genus is still needed.