This paper presents new findings on oligochaete species inhabiting Polish brackish waters. Identification of 455 specimens collected in September 2013 and July 2014 during the macrozoobenthos survey in the Port of Gdynia (the Gulf of Gdańsk, the southern Baltic Sea, Poland) showed the presence of six species belonging to two subfamilies Naidinae and Tubificinae.
A new locality of the Asian thermophilic aquatic oligochaete Branchiura sowerbyi Beddard, 1892(Oligochaeta, Naididae) was recorded in the Upper Oder River. Until now, this species has been only noted in a few localities in Poland: in the Szczecin Lagoon at the mouth of Oder River to Baltic Sea, in the heated Konin lake system (West Poland) and in the middle course of the Oder River. In our study, B. sowerbyi was found on one site (108 km of the river course) that is located more than 400 km from its previous recordings in the Oder River. This finding may show that B. sowerbyi has spread upstream. It should be noted that, as a rule, low abundance of this species may be the reason for the small number of its recordings, so further studies related to distribution and impact of B. sowerbyi on native oligochaetes are needed.
The highest density of macrofauna was recorded in a muddy habitat, and the highest biomass (d.w.) in a stony one. Only Naididae, Hydracarina, young larvae of Trichoptera, and large specimens of Gammarus spp. preferred a transitional habitat (mud-covered stones). Of the 25 identified species of Oligochaeta especially three dominant species (Nais bretscheri, N. pardalis, and N. communis) were most numerous in the transitional habitat. Downstream the species diversity of Oligochaeta increased and the composition of the community changed.
Oligochaetes constituted 91-98% of the numbers and 78-97% of the biomass of the macrofauna, the remaining part were Chironomidae, while Chaoboridae, Sphaeridae, Ephemeroptera, and Coleoptera occurred sporadically. The highest density (14.5 thous. indiv. m-2) and biomass (13 g m-2) were observed near the dam. 14 species of the Oligochaetes (the most numerous being Potamothrix hammoniensis, Limnodrilus claparedeanus, and L. hoffmeisteri) and 5 taxa of Chironomidae were determined in the samples.
We have proved highly significant differences in glucose concentration and activity of alpha-amylase in haemolymph of two growth classes of Planorbarius corneus with width of shell smaller and equal or greater than 20 mm, respectively. Both these parameters were higher and were characterized by greater range of individual variability in snails with smaller width of shell. Any differences in levels of total protein and haemoglobin in haemolymph of these animals, in comparison with adult individuals, were not observed. Effect of infection of the pulmonary cavity of investigated snails with Chaetogaster limnaei limnaei on the examined parameters was not ascertained.
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