Micro- and meiobiota patterns in glacier driven stream habitats

Glacier-fed rivers are among the most sensitive and endangered habitat types nowadays. Their upper reaches are located within areas of economic interest (e.g. skiing and glacier skiing, hydropower generation), but also within protected areas such as, for example, National Parks worldwide (e.g. Hohe Tauern, Pyrenees, Rocky Mountains). The majority of glacial river studies has focused on the macrozoobenthos. Thus, this study presents a comparison of the widely neglected stream microand meiobenthos (MMB) among different glacial-fed stream reaches driven by two different glacier catchments: the Möll River Catchment (MC) and the Kleinelendbach stream catchment (KC). The catchments differ in catchment and glacier area, and glacier retreat patterns. The stream reaches comprised different habitat types such as the glacier source and extreme harsh glacial stream main channels, but also benign, less glacier influenced side channels. Their ages (years since deglacierization) ranged from 0 to ~ 150 years. They were within the protected area of the Hohe Tauern National Park. The regional diversity of the MMB (taxa numbers of fungi, algae, protists, nematodes, rotifers, invertebrates) was generally high in both catchments (MC: 270; KC: 291). The local (stream reach) diversity was also relatively high, but taxa numbers varied considerably between reaches and ranged from 64 – 195. Highest taxa numbers were recorded for benign stream habitats of the KC (195) and the MC (172). The latter was within the Sandur area downstream the margin of the Pasterze glacier. The benign sites represented not only local hot spots of diversity but also hot spots of ecological functionality with regard to the broad spectrum of abundant organisms, comprising primary producers (autotrophic flagellates, cyanobacteria, diatoms and other algae), decomposers (bacteria, fungi) and diverse consumers (heterotrophic flagellates, protists, nematodes, rotifers, copepods, tardigrades). ANOSIM resemblance analysis revealed similarity of fungi, protists and rotifers, and dissimilarity of bacteria, flagellates, diatoms and nematodes between the different stream reaches. The perspectives of ongoing glacier retreat and expected alterations of glacial-fed rivers may have various consequences for the MMB: thermal and hydrological changes along main river channels will represent adaptive challenges to these organisms, whereas drying of side arms and surrounding wetlands will lead to regional extinctions. The latter would represent an enormous loss of diversity that may affect ecological processes and services of alpine areas. But actual habitat changes and their effects on biodiversity as well as on ecological processes and services of alpine glacier catchments clearly need further investigations.