Microhabitat preferences in springs, as shown by a survey of nematode communities of Trentino (south-eastern Alps, Italy)

Ninety-four Alpine springs in Trentino, from 170 to 2792 m a.s.l., were studied and compared for their nematode communities. No nematode species appeared typical for Alpine springs (crenobionts or crenophiles); all the identified species were common in freshwater habitats, with a wide geographical range on a continental scale. The only notable, rare species was Eumonhystera tatrica Daday, 1896, a very small nematode that has apparently never been found since it was first described. Eighty springs with more than 7 specimens were retained for statistical analysis. Distinctness indices Δ+ and Λ+ showed that only a few springs exceeded the funnel limits for such indices. The relationships between habitat features and community composition, and nematode ecology (c-p value, size, trophy) were investigated. The major abiotic factors influencing nematode community composition were water temperature and lithology (carbonate vs. crystalline). In addition, nematode communities from mosses differed from those sampled from other substrata in the same spring. The nematode-based Maturity Index increased with crenic water temperature, in contrast to other indices, such as Shannon diversity and Berger-Parker index, suggesting that r-strategist nematode species replace K-strategists along the temperature gradient. Lithology did not alter species richness, but the relative abundance of species present on carbonate and in non-carbonate substrata varied. The 4th-corner analysis showed significant correlations between temperature and species trophic group. In conclusion, nematodes are good ecological indicators of polluted vs unpolluted waters, but, at least in this case, cannot be used to differentiate between unpolluted habitats such as Alpine springs.