Experimental manipulation of the winter surface ice layer: the effects on a High Arctic soil microarthropod community

The effect of patch size on the tolerance of the soil microarthropod population to an experimentally induced environmental catastrophe, a thick surface ice layer, was studied at a High Arctic site (78 degrees 55'N, 11 degrees 53'E). Such an ice layer currently occurs infrequently; however, climate change models suggest that the occurrence of such an ice layer is likely to increase in frequency. The experimental approach was a factorial design with two patch sizes, an icing treatment and controls. A thin layer of natural ice was present even in the controls and this was treated as a covariate in the analysis. The soil microarthropod fauna at the experimental site consisted of five species of Collembola and seven species of oribatid mite. The experimental surface ice layer reduced the total number of the soil microarthropods studied by 50%; however, mortality differed between mites and Collembola and species within the two taxonomic groups. Mites were very resistant and showed no significant change, Collembola more sensitive (the populations of Hypogastrura tullbergi declined by 56% and Folsomia quadrioculata by 54% in the iced treatment plots). The thin annual surface ice layer seemed to have an additional effect on H. tullbergi and the mite Lauroppia translamellata. That such a thin ice layer could reduce survival was unexpected and could play an important role in determining the extreme patchy distribution of arctic soil animals.