Gusakov V.A. 2011. [Tardigrades in bottom meiofauna in different waterbodies of the Upper Volga Basin] // Invertebrate Zoology. Vol.8. No.1: 37–56 [in Russian, with English summary].

Institute for Biology of Inland Water, Russian Academy of Sciences, Borok, Yaroslavl Area, 152742, Russia; e-mail: gva@ibiw.yaroslavl.ru

KEY WORDS: Tardigrada, Upper Volga, species composition, quantitative parameters, seasonal and long term dynamics.

ABSTRACT: This paper describes the results of investigations of tardigrades as a part of meiobenthos in different waterbodies (rivers, lakes, reservoirs) of the Upper Volga basin. To the present time 21 species of freshwater Tardigrada have been found in the region. In the investigated waterbodies the most widespread and numerous species were Pseudobiotus megalonyx (Thulin, 1928), Isohypsibius granulifer Thulin, 1928, Dactylobiotus selenicus Bertolani, 1981 and Thulinia ruffoi Bertolani, 1981. The first of them is met in the majority of biotopes. In the reservoirs the tardigrades can make up over 50% of the total number and 30% of meiobenthos biomass even at a high abundance of other organisms. The maximal population density was registered for P. megalonyx in the Gorky Reservoir — 225.7 thous. ind./m2 and 3.5 g/m2. The seasonal and long term abundance dynamics of tardigrades (in the Rybinsk Reservoir as an example) are complicated. In some years they are almost completely absent in samples, in other — reach a significant amount. The maximal number of tardigrades individuals occurs in mid March – late June. In different years in this period 1–3 peaks of abundance are registered for various species, the greatest — usually, in May at temperature ~12–15°C. Changes in the abundance dynamics of the taxonomic group and separate species are similar both in profundal and open inshore zone, hence they are determined, mainly, by climatic factors. During the autumn-winter decrease of the reservoir level in the drained and frozen sediments of littoral P. megalonyx, D. selenicus and I. granulifer at mature age retain their vitality not less than for 7–11 weeks. The aggregated distribution in biotopes is typical for tardigrades, apparently, owing to low motility. Even under similar living conditions the density of populations differs by orders of magnitude. Because of considerable fluctuations of  tardigrades abundance by years, seasons, biotopes and «within» similar biotopes long term investigations are necessary for obtaining reliable data on their distribution and population dynamics in waterbodies.

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