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 popula tion to an experimentally induced environmental catastrophe, a thick surfac e 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 c hange models suggest that the occurrence of such an ice layer is likely to increase in frequency. The experimental approach was a factorial design wit h 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 i n the analysis. The soil microarthropod fauna at the experimental site cons isted of five species of Collembola and seven species of oribatid mite. The experimental surface ice layer reduced the total number of the soil microa rthropods studied by 50%; however, mortality differed between mites and Col lembola and species within the two taxonomic groups. Mites were very resist ant and showed no significant change, Collembola more sensitive (the popula tions of Hypogastrura tullbergi declined by 56% and Folsomia quadrioculata by 54% in the iced treatment plots). The thin annual surface ice layer seem ed to have an additional effect on H. tullbergi and the mite Lauroppia tran slamellata. That such a thin ice layer could reduce survival was unexpected and could play an important role in determining the extreme patchy distrib ution of arctic soil animals.