Arthropod colonisation of a debris-covered glacier

Abstract

The largest debris-covered glacier in the Alps (Miage Glacier, western Italian Alps) has been studied to explore the effects of debris-cover extent and depth on the spatial distribution of ground-dwelling arthropods. A multitaxa approach has been used to compare taxa richness and distribution to the functional role (dietary habits) of each taxon along the glacier tongue. Spiders and ground beetles have been studied in detail. Taxa richness declines with distance from the wooded sites (in front of the glacier tongue) to those above the glacier tongue. At each of the supraglacial sites, spiders, ground beetles, aphids, springtails and flies were found. A change in the dominance of the different functional roles was observed along the tongue. Wooded sites are characterised by predatory (e.g. spiders, beetles), detrivore (e.g. springtails and certain flies), phytophagous (e.g. aphids, certain beetles) and parasitoid (e.g. certain wasps) assemblages, whereas at the debris-covered sites, aphids, flies and springtails are likely to be prey for spiders and beetles. The species richness of the predominant predators (spiders and beetles) shows a positive relationship with vegetation cover and debris thickness. Two mutually exclusive spider and ground beetle assemblages were found; one within the debris cover and one within the wooded sites. In our opinion, debris-covered glaciers are acting as a refuge area for the cryophil stenotherm species living at higher altitudes which descend the glacial tongue to lower elevations. A similar hypothesis supports the biogeographical interpretation of the distribution of many boreo-alpine relict species in the Alps. We discuss our results in the light of possible future scenarios which suggest an increase in debris cover with global warming.

Bacterial community structure on two alpine debris-covered glaciers and biogeography of Polaromonas phylotypes

“…Chitinophagaceae and other chitinolytic bacteria dominated the Bacteria of debris-covered glaciers A Franzetti et al microbial communities of Antarctic soils and glacier forefields (Brankatschk et al, 2011;Ganzert et al, 2011). Chitin provides both C and N to the microorganisms (Moorhead et al, 2012) and may be supplied by arthropods, whose presence was already documented on the Miage glacier (Gobbi et al, 2011), and by fungi, which occur in recently deglaciated soils (Zumsteg et al, 2012). Interestingly, arthropods' communities showed a turnover along the Miage glacier tongue, and richer and more structured communities occurred close to glacier terminus (Gobbi et al, 2011).…”

“…Chitin provides both C and N to the microorganisms (Moorhead et al, 2012) and may be supplied by arthropods, whose presence was already documented on the Miage glacier (Gobbi et al, 2011), and by fungi, which occur in recently deglaciated soils (Zumsteg et al, 2012). Interestingly, arthropods' communities showed a turnover along the Miage glacier tongue, and richer and more structured communities occurred close to glacier terminus (Gobbi et al, 2011). Despite the fact that no data on the concentration of chitin in the debris cover of DCGs are available, we speculate that chitin might represent a relevant fraction of the OC in the debris of DCGs.…”

“…As a result, the glacier surface is covered by a continuous debris layer, whose thickness generally increases toward the glacier terminus. The long transport on the glacier surface allows debris weathering and alteration, and its colonization not only by microorganisms but also by animals (for example, arthropods) and plants (Pelfini et al, 2007(Pelfini et al, , 2012Caccianiga et al, 2011;Gobbi et al, 2011). Ecological communities therefore exist on the surface of DCGs, and may be structured according to a chronosequence, with communities increasing in complexity towards the glacier terminus (Gobbi et al, 2011).…”

Climate change and its impact on epigean and hypogean carabid beetles

“…Primary successions on glacier foreland barren soils are surely more "inviting" topics because in such context the evolution of vegetation can be followed in parallel with the development of an animal community and the glacier watch services can provide for exact dating the steps, moreover, human disturbance is totally absent. Carabid beetles play a fundamental role in colonizing the extremely cold habitats above the treeline and are able to settle on "black glaciers" (38). They constitute in competition with spiders the main predatory component of such communities and live here primarily at the expense of the decomposition food chain, but intraguild predation constitutes another important food source (40).…”

“…Nevertheless, the picture get complicated by the ability of some wingless species to live on the "black glaciers", i. e. the debris covered glacier tongues. This poorly investigated phenomenon has studied on the Miage Glacier (38), where a predator dominated community of spiders and a "cryophilic" Nebria species is living at the expense of aphids, flies and springtails. Black glaciers are probably of high importance for the survival of low temperature adapted species in the mountains (38), where they offer cool and stable subterranean spaces rich of organic substance and prey, a process that is known to favour the origin of alpine endemic invertebrates (39).…”