Habitat comparison of Mideopsis orbicularis (O. F. Müller, 1776) and M. crassipes Soar, 1904 (Acari: Hydrachnidia) in the Krąpiel River

Ecological studies of water mites have a very long tradition. However, no explicit data have been obtained to date with regard to specific ecological parameters defining autoecological values for particular species, and therefore such values have not been compared between closely related species. The present study is an attempt at making such comparisons between two closely related species: Mideopsis orbicularis and Mideopsis crassipes. Both species are psammophilous; M. orbicularis prefers stagnant waters, while M. crassipes prefers running waters. The research was conducted during 2010 in 89 localities distributed along the Krąpiel River and in water reservoirs found in its valley. The two species were collected solely in the river, where they were found in 26 localities and only these localities were analyzed. Until now M. crassipes was characterized as a species preferring rather fast-flowing habitats, and M. orbicularis as preferring slow water habitats, i.e. isolated still-water bodies. In this study both species preferred slow flow water habitats: 77.5% (225 individuals) of all M. orbicularis specimens and 67.3% (318 individuals) of all M. crassipes specimens were collected in isolated still-water bodies. The only correlations identified between water mite occurrence and water quality were the positive one between the abundance of M. orbicularis and water temperature, the negative one between the abundance of this species and BOD5. There were also some correlations with substrate, including the positive correlation between occurrence of M. crassipes and sandy bottom. M. orbicularis was also encountered on organic bottoms and among water plants.