The environmental requirements of Crunoecia irrorata (Curtis, 1834) (Trichoptera: Lepidostomatidae) and the potential of the species for use as an indicator: an example from the Vistulian glaciation area

The caddisfly Crunoecia irrorata is a wide-spread species in Europe and inhabits permanent spring areas with pristine or moderately disturbed habitat conditions. However, the pattern of its distribution on the national scale as well as detailed preferences toward water properties are still insufficiently known. To complete this knowledge we analysed at first the distribution of this species in Poland which showed that its extent involves the whole territory, however, with sparse occurrence in most regions and with large areas where the species has not been observed yet. The data compilation also showed that the species’ frequency of occurrence is highest in the central-western region of Poland. Furthermore, its frequency of occurrence decreased towards the east and the northeast. Because the highest frequency of occurrence of this species was found in central-western Poland, the spring sites in this region were used as a model area for the analysis of the hydrochemical conditions associated with the species (25 parameters). The results of the study showed that C. irrorata strongly prefers habitats with low nitrate (NO₃) and chloride (Cl) concentrations. In detail, a regression model showed that the probability of occurrence of C. irrorata was only 5 % at concentrations of 32 mg L^-1 NO₃ and 35 mg L^-1 Cl. In contrast, high concentrations of heavy metals (zinc, lead, cooper, chromium, and cadmium) as well as of total iron and manganese did not significantly influence the presence of this species. In conclusion, environmental assessments relating to human health and landscape health can use C. irrorata as an indicator species for biogenic and salt pollution, but the species is not a potential indicator of heavy metals in spring water. Therefore, information on the presence of C. irrorata can serve to preserve crenic ecosystems and their assemblages and can be used to prevent anthropogenic contamination of these ecosystems.