Effects of locality and stone surface structure on the distribution of Collembola inhabiting a novel habitat – the stone-ice border on an alpine glacier

Supraglacial zones worldwide serve as suitable habitats for psychrophiles, including metazoans. The present study investigates whether the occurrence and abundance of springtails in water films under stones on the Forni Glacier in the Alps is affected by: a) the stone's location (on bare ice, in supraglacial streams, in the glacier forefield, on the medial moraine), b) the stone's distance from the glacier terminus, c) the roughness of the stone's surface, and d) the stone's position with respect to the surface of the ice (inclination). The Forni Glacier is inhabited by representatives of dark-pigmented Isotomidae. The study demonstrates that the density of springtails inhabiting the underside of stones located on the ice came to 155,000 individuals per one square meter of a stone surface with their abundance showing no relation to the stones' distance from the glacier terminus. Moreover, springtails occurred more frequently and more abundantly under stones located on bare ice than under those in supraglacial streams, the medial moraine or the glacier forefield. The roughness of stone surface facing the ice had a positive effect on animal counts, while its inclination had no strong effect. We estimated that the total abundance of springtails under stones on the Forni Glacier's tongue may reach 10.8 million individuals. Since many springtails are hidden in supraglacial gravel and medial moraine, the dry biomass of animals visible under stones comprises at least 105.7 g.