Water beetles (Coleoptera) of small reservoirs in the neighborhood of Swinoujscie (NW Poland)

The present paper describes a diversity of water beetle communities inhabiting five small water reservoirs, located in the north-western part of Wolin Island, near of Świnoujście city (Poland). The analyzed aspects of beetle communities included differences in species composition and the abundance of beetles in various water bodies, taking into account such features of the reservoirs as their size, periodical character, maximum depth, structure of vegetation and the percentage of surface shaded by plant canopy. In total, 60 species of beetles were recorded in the reservoirs, including three species endangered with extinction in Poland, i.e. Haliplus apicalis , H. furcatus , H. variegatus, and one species critically endangered with extinction in Poland, namely Spercheus emarginatus. The largest number of species (42) and individuals (1294) was found in a periodical, relatively big, open and shallow pool situated in a lowland peat bog and covered with soft submerged vegetation. However, the population of beetles found in this location was strongly dominated by two species, Hydrochara caraboides and Hygrotus decoratus, which resulted in the lowest biodiversity coef ficient (H` = 0.705) in comparison with the other investigated reservoirs. In permanent but significantly shaded reservoirs, the number of recorded species was almost two times lower and the abundance of beetles was even eight times lower. However, in such water bodies the diversity coef icient had the highest values (0.981 < H` > 0.991). As fa As far as the environmental aspects were concerned, it was discovered that the most significant were the size of the reservoir and its permanent/non-permanent character. Only the differences in size reached the level of statistical validity (p = 0.040), explaining 34.8% of cases of species variability. The similarity among beetle communities inhabiting particular reservoirs varied from 31.63% to 53.3% and was connected with ecological similarity of the investigated water bodies.