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 (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 (Trägårdh, 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.

In total, 11 samples, each with a volume of 500 cm³ (ca 100 cm² in area and 5 cm deep), were collected by hand on 12 June 2017 from two types of forest microhabitat (Figure 2), (A) water-soaked Sphagnum mosses at the edge of a pool (five samples) and, (B) other mosses growing on the medium-wet forest floor nearby (six samples). Mites were extracted using modified Tullgren funnels for 14 days into 90% ethanol and sorted out from the samples under stereomicroscope. Oribatida were mounted on cavity slides in 90% lactic acid (AnalaR NORMAPUR, VWR Chemicals, Belgium) and adult specimens were identified using the keys [15–18], while juveniles were identified based on other publications. Mesostigmata were mounted on permanent slides in PVA mounting medium (lactic acid, poly vinyl acetate and phenol solution, BioQuip Products, Inc., Compton, CA, USA) and identified following publications.