Abstract
High biodiversity is a prerequisite for the integrity, stability, and functioning of global aquatic ecosystems, but it is currently subject to anthropogenic threats. Small freshwater bodies with high habitat diversity are essential to sustain regional biodiversity, but speciesinventory and biodiversity are largely overlooked, especially in mountainous regions. In the Italian Alps, obligate assessments of fresh-water biota (e.g., for the European water framework directive, WFD) are usually done in larger rivers or lakes only, which is why manytaxa from small freshwater habitats might have been overlooked so far. Here we summarize and discuss the efforts to record aquatic in-vertebrates within the framework of so-called “Biodiversity Days”, organized since 2001 at 13 different sites located across the NorthItalian province of South Tyrol. These events with voluntary participation of scientists and naturalists from universities and environmentalagencies led to the detection of 334 benthic invertebrate taxa in streams and lakes (mostly at species or genus level), whereby highertaxa richness was found in streams. The overall hierarchy of species numbers within invertebrate orders or families corresponded tothat of other Alpine regions (groups richest in taxa were Chironomidae and Trichoptera) and these Biodiversity Days contributed tobiodiversity research of that region in detecting 167 additional taxa. Besides analyzing yearly gains in the regional taxa inventory, wepredict that future surveys will lead to new discoveries of aquatic taxa for that province (i.e., current modeling estimates a regional in-ventory of more than 600 taxa). However, specific surveys in hitherto unconsidered habitats, such as morphologically modified or urbanwaters, might reveal even more taxa than currently estimated. Besides characterizing the invertebrate fauna of this region and providinga first reference list for future monitoring projects in the same region, this work demonstrates that such Biodiversity Days can contributeto biodiversity research.