Contrasting Distribution Patterns of Subfossil Testate Amoebae and Cladocerans in a Stratified Freshwater Lake and Their Significance for Bioindication and Palaeoreconstructions

ABSTRACT Testate amoebae and cladocerans occur worldwide in lacustrine habitats and are well represented in contemporary bottom sediments and Holocene fossil strata. They are widely used as proxies for palaeoecological reconstructions and bioindicators in modern ecosystems. However, existing knowledge on the distribution patterns of these groups in the bottom sediments of stratified freshwater lakes is still limited, thereby reducing the reliability of predictions. The aim of this study was to investigate the extent to which changes in the diversity and species composition of testate amoeba and cladoceran communities reflect changes in the environmental conditions along the depth gradient in a stratified freshwater lake. Samples were collected in Lake Glubokoe (East European plain, the Smolensk‐Moscow upland) with a depth range of 0–32 m and intervals of 3 m along two transects, resulting in a total of 69 samples from 33 sites. We distinguished three testate amoeba assemblages and four Cladocera taphocenoses related to littoral, sublittoral and profundal zones. In both the littoral and profundal zones, the dominant species in each group exhibited similar, yet group‐specific ecological preferences within each benthic zone, whereas in the sublittoral zone, the ecological preferences of dominant species in each group were contradictory. The distribution patterns of benthic testate amoebae were determined by the local hydrological conditions in the bottom sediments (i.e., temperature, productivity of habitats, BGA‐PC and oxygen concentration). The distribution patterns of planktonic cladocerans reflected the trophic status of the whole lake. Changes between littoral and profundal taphocenoses were driven by the presence of waterplants and by the productivity of habitats. This study showed that species composition and diversity of testate amoebae and cladocerans were influenced by habitat productivity. Changes in species composition of unicellular freshwater hydrobiont communities in the littoral, sublittoral and profundal were also influenced by a number of zone‐specific hydrochemical variables, whereas changes in multicellular communities were associated with the presence or absence of waterplants and horizontal movement of physical remains. Variables associated with changes in species composition of testate amoebae and cladocerans should be taken into account in palaeoreconstructions when developing and interpreting transfer functions for both groups.