A Forest Pool as a Habitat Island for Mites in a Limestone Forest in Southern Norway

Forest water bodies, e.g., pools, constitute 'environmental islands' within forests, with specific flora and fauna thus contributing considerably to the landscape biodiversity. The mite communities of Oribatida and Mesostigmata in two distinctive microhabitats, water-soaked Sphagnum mosses at the edge of a pool and other mosses growing on the medium-wet forest floor nearby, were compared in a limestone forest in Southern Norway. In total, 16,189 specimens of Oribatida representing 98 species, and 499 specimens of Mesostigmata, from 23 species, were found. The abundance and species number of Oribatida were significantly lower at the pool, while the abundance and species richness of Mesostigmata did not differ. Both the communities of Oribatida and of Mesostigmata differed among the microhabitats studied and analysis showed significant differences between the community structures in the two microhabitats. The most abundant oribatid species in Sphagnum mosses was Parachipteria fanzagoi (Jacot, 1929), which made up over 30% of all Oribatida, followed by Atropacarus striculus (C.L. Koch, 1835) and Tyrphonothrus maior (Berlese, 1910) (14% and 12% of Oribatida, respectively). Among Mesostigmata Paragamasus parrunciger (Bhattacharyya, 1963) dominated (44% of Mesostigmata), followed by P. lapponicus (Tragardh, 1910) (14% of Mesostigmata). Most of these species, except P. lapponicus, were either absent or very uncommon in the other microhabitat studied. The specific acarofauna of the forest pool shows the importance of such microhabitats in increasing forest diversity. In addition, a quarter of the mite species found had not been reported from Norwegian broadleaf forests before, including five new species records for Norway and four new to Fennoscandia, all found in the medium-wet microhabitat. Most of these species are rarely collected and have their northernmost occurrence in the studied forest.