Distribution and diversity of Tardigrada along altitudinal gradients in the Hornsund, Spitsbergen (Arctic)

Two transects were established and sampled along altitudinal gradients on the slopes of Ariekammen (77 degrees 01'N; 15 degrees 31'E) and Rotjesfjellet (77 degrees 00'N; 15 degrees 22'E) in Hornsund, Spitsbergen. In total 59 moss, lichen, liverwort and mixed moss-lichen samples were collected and 33 tardigrade species of Hetero- and Eutardigrada were found. The alpha diversity ranged from 1 to 8 per sample; the estimated number of species based on all analysed samples was 52 +/- 17 for the Chao 2 estimator and 41 for the incidence-based coverage estimator. According to the results of detrended canonical correspondence analysis, altitude and type of substratum were the most important factors influencing tardigrade communities in the investigated area. Macrobiotus crenulatus, M. hufelandi hufelandi and Hypsibius pallidus dominated in the lower elevations, whereas Echiniscus wendti and E. merokensis merokensis prevailed in samples from higher plots. Macrobiotus islandicus islandicus was collected most often from mosses collected from rock whereas Isohypsibius coulsoni from mosses collected from soil. Analyses of covariance were employed to test for differences in species richness between the transects in relation to altitude. Contrary to expectations, there were significant differences in species richness between the transects, but richness was not significantly related to altitude. Interestingly, significant effects of colonies of seabirds, little auk (Alle alle), on the tardigrades communities were detected. Additionally, in one of the samples first ever males of Milnesium asiaticum were found. Their measurements and microphotographs are provided herein.