Micro- and meiobenthos in glacial river systems

Adequate information on major components within benthic food webs is a prerequisite for a better understanding of underlying processes such as nutrient cycling and energy transfer. Nevertheless, glacial river system research is biased mainly towards the macrofauna and has widely neglected the meiofauna and other microbiota within benthic food webs. This study is designed to provide a first, more relevant approach to benthic food webs in glacial rivers by investigating the benthic meiofauna together with the benthic microbiota (i.e. bacteria, algae, aquatic hyphomycetes, protists). The spatio-temporal variation of community parameters of the respective groups will be obtained for local, regional and temporal scales: we will sample disparately harsh riverine habitats (meta- and hypokryal reaches, and moderate reaches accompanying the hypokryal) in two catchments with varying degree of (de-)glaciation before, during, and after the glacial ablation period. The significance of different distribution as well as the effect strength of habitat characteristics (water temperature, pH, specific conductivity, habitat stability, biotic relations, stream age) but also of biotic groups on each other will be tested. In doing so, we will draw conclusion about habitat templets (filters) determining the benthic biota. Alpha, beta and gamma diversity will be discussed as parameters giving additional information about community similarty and changes (temporal, seasonal) and potential interaction between species and groups.

World-wide retreat patterns of glaciers bear witness for their sensitivity to climate change. The ongoing losses of ice masses lead to changes in glacier-fed rivers, whose abiotic conditions (i.e. water temperature, discharge, stability, turbidity) are highly dependent from glacier activities such as ice melt in summer (glacier ablation) and ice formation outside the ablation periods (glacier accumulation - a years-long process). The effects of these abiotic changes on the biota of glacier rivers are poorly understood, because science knows little about essential components living in the sediments of glacier rivers, namely the meiofauna (rotifers, nematodes, copepods, tardigrades) and the microbiota (bacteria, nanoflagellates, protists, algae ) in the following as MMB. But particularly these MMB are of major importance for the functionality (nutrient cycling, water quality).In an unprecedented approach, the present study documents the development of these hitherto widely neglected organisms along contrasting river reaches of two highly contrasting glacier catchments in the Austrian Alps - the Möll River catchment (MC, Pasterze glacier), and the Kleinelendbach stream catchment (KC, Kleinelendkees glacier). They differ in catchment area (km) and ice cover (%) as follows: MC - 36km, 61%; KC - 12km, 25%. The summed length retreat since 1998 has been massive at the MC with about 400m (Pasterze) and minor at the KC with about 30m (Kleinelendkees glacier). This difference is reflected in successional stages (time since deglacerization) of the investigated river reaches by MCs younger (0 - ~ 50 years) and KCs older (~ 30 to ~150/200 years) reaches. With regard to all these spatio-temporal aspects of (de)glacierization, the MC is considered to be an overall harsher environment than the KC, and considered together, these two catchments offered a model with which to study the relation between the different stages of changes and harshness in glacier catchments and the basic hydrological and biological patterns thereof.With 270 (MC) and 291 (KC) taxa, the difference in the overall regional diversity - comprising species and genera of fungi, algae, protists, nematodes and rotifers - was lower than expected with respect to the differences of harshness and successional stages between the MC and the KC. Furthermore, catchment contrasts were not a major determinant of resemblance patterns of the most important MMB groups (i.e. bacteria and nanoflagellates, protists and algae, fungi, nematodes, and rotifers). The rapid glacier retreat at the MC established a harsh proglacial but also a benign floodplain area, which distinctly supported the development of complex MMB communities (high abundances and taxa richness). Nevertheless, comparisons of similarly aged riverine habitats evidenced developmental suppression of the MMB (64 taxa; MC) by the rapidly retreating MC glacier, unlike the moderate glacial retreat in the KC (130 taxa). The different catchment characteristics formed river reach conditions ranging from harsh to benign, which were well represented by the glaciality index (GI; integrating water temperature, electrical conductivity, and stream bed stability in one single measure). The strong relationship between MMB abundances and diversity and this index points out that decreasing harshness (decreasing glacier influence) generally depress the MMB. Nevertheless, such causalities were strongest for nematode abundances and maturity. Finally, nematodes turned out to be a potential suitable indicator for distinct riverine conditions (abiotic, microbiota resources) developing along with climate induced changes in glacier catchments.