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It was observed that the density values of Gastrotricha fauna expressed by the number of specimens in 1 cm3 of sediment or by the number of specimens falling on 1 m2 of the bottom area, obtained by various sampling methods, are comparable. For samples drawn with a vessel from the surface layer of the sediment it was shown that a multiplier of 60 000 was essential.
The density and dominance of benthic and epiphytic fauna of selected meioinvertebrate groups were studied in various types of standing water in eastern Poland: two lakes (mesotrophic and polytrophic) and two small water bodies (an oligotrophic pond and a peat-hag). The plants from which the fauna were collected included: Ceratophyllum demersum L., Elodea canadensis Michx., Hydrocharis morsus-ranae L., Myriophyllum spicatum L., Nuphar lutea (L.) Sibth. (i) Sm., Potamogeton natans L., and Stratiotes aloides L. In the taken material, the density and dominance structure of benthic and epiphytic fauna of the taxa Turbellaria, Gastrotricha, Rotifera, and Nematoda were estimated. Total density of the studied phyla in bottom sediments and on elodeids fluctuated from 1315.0 to 3156.0 10³ indiv. m⁻², and from 2078.0 to 3954.0 10³ indiv. m⁻², respectively. Mean density of meioinvertebrates per 100 g dry weight of plants in the studied waterbodies amounted to from 125.8 to 289.0 10³ indiv. 100 g⁻¹ d.w. The density of meioinvertebrate fauna of elodeids was higher than in bottom sediments in all studied reservoirs and the differences were statistically significant. Epiphytic meioinvertebrate fauna in Lake Bikcze of high trophic level shows low similarity to the mesotrophic one, and to the oligotrophic pond, but shows high similarity to the peat-hag. The development of the meioinvertebrate community on elodeids is mainly affected by the trophic status of the reservoir and not by the character of vegetation.
Composition and abundance of Gastrotricha in lake psammon were studied and compared with those from other lake habitats. Samples were taken from April till October 2004 from 3 sites at the edge of zone frequently wetted by waves (hygropsammon) in a deep (38 m) mesotrophic lake situated in Łęczyńsko-Włodawskie Lakeland (south-eastern Poland). A total of 11 gastrotrich species belonging to Chaetonotidae family were found. Three species: Lepidodermella squamata Dujardin, Chaetonotus macrochaetus Zelnika i Ch. heideri Brehm dominated (52%) in total abundance. According to the previous studies the number of species occurring in bottom sediments of the same lake was higher by 11–14 species. Species diversity index H’, amounted 2.19 being lower than that calculated for the gastrotrichs of inshore bottom and littoral sediments (2.88 and 2.58, respectively) and similar to the value given for epiphytic fauna (2.01) of that lake. The fauna of psammic Gastrotricha showed the greatest similarity (38%) to epiphytic fauna of that lake as measured by the index of homogeneity. Peak densities of psammic Gastrotricha were found in May (37.5 10³ ind. m⁻²) and in September (32.8 10³ ind. m⁻²) and marked decrease of density was observed in August and October (18.1 10³ ind. m⁻² and 13.6 10³ ind. m⁻², respectively). Mean density and biomass were 25.35 10³ ind. m⁻² and 3.8 mg m⁻² respectively. Density and biomass of Gastrotricha were by two orders of magnitude lower in psammon than in bottom sediments of the lake.
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