Hydrobiologia 453/454: 309–324, 2001. R.M. Lopes, J.W. Reid & C.E.F.Rocha (eds), Copepoda: Developments in Ecology, Biology and Systematics. © 2001 Kluwer Academic Publishers. Printed in the Netherlands. 309 Distribution and ecology of copepods in mountainous regions of the Eastern Alps C. D. Jersabek 1,4 , A. Brancelj 2 , F. Stoch 3 & R. Schabetsberger 1 1 Institute of Zoology, University of Salzburg, A-5020 Salzburg, Austria 2 National Institute of Biology, 1000 Ljubljana, Slovenia 3 Museum of Natural History, Verona. Current address: Viale XXV Aprile, 24, I-34015 Muggia (Trieste), Italy 4 Present address: Academy of Natural Sciences, Biodiversity Dept., 1900 Benjamin Franklin Parkway, Philadelphia, PA 19103, U.S.A. E-mail: jersabek@acnatsci.org Key words: Calanoida, Cyclopoida, Harpacticoida, alpine waters, altitudinal distribution, biogeography, ecology Abstract Copepod species richness, patterns of distribution and composition of assemblages were evaluated in high-altitude sites in the Eastern Alps. Diverse habitats were sampled in 160 lentic water bodies from different geologic areas, ranging from acid bog ponds to alkaline karst waters and from small temporary puddles to deep lakes. The altitud- inal range comprised all mountainous regions from the montane (1290 m a.s.l.) to the alpine (2886 m a.s.l.) zone. Forty-four species were recorded, with the harpacticoids being the richest group. Although most species occupied a wide altitudinal range, some stenotopic mountain forms were restricted to alpine habitats. The most widespread taxa were Acanthocyclops vernalis, Eucyclops serrulatus, Bryocamptus rhaeticus, Arctodiaptomus alpinus and Cyclops abyssorum tatricus. All species found were listed along with notes on their distribution, ecology and patterns of coexistence. There was both a marked change in species composition and a decline in species richness from hardwater habitats in the Limestone Alps to softwater sites in the Central Alps. Copepod taxocoenoses were most diverse in montane limestone lakes and impoverished with increasing altitude. Copepods and sampling sites were ordinated using canonical correspondence analysis (CCA), and copepod assemblages were defined in relation to physical and chemical parameters, habitat type and presence/absence of planktivorous fish. Planktonic species were largely absent from lakes with introduced fish. Although calanoid associations were common, coexisting diaptomids were rare, suggesting a strong interspecific competition between these predominantly filter feeders. Most copepods found are common eurytopic or cold stenothermal, but some exhibit peculiar disjunct patterns of geographical distribution, and others are apparently restricted to the Alps. Some species are discussed in more detail from a zoogeographical point of view. A complete checklist of copepods recorded to date from high-altitude sites in the Eastern Alps is provided. Introduction High mountain areas in the Alps are among those zoogeographical regions in which the latest post- glacial colonization events occurred. Most lakes are younger than 10 000 years, and several are still in statu nascendi, directly influenced by retreating glaciers. Thus, recent distribution patterns of aquatic organisms are a young post-glacial event, and communities are frequently in an early stage of succession. The East- ern Alps consist of a complex pattern of geological strata that impose different limnological conditions on aquatic habitats. These are further determined by altitudinal and north-south changes in climate, soils and vegetation. Basically, two major limnological provinces may be distinguished from the different sol- ubilities of bedrocks: lakes on primary rock in the Central Alps tend to have ion-poor, soft water, while lakes in the Limestone Alps and eastern Dolomites are rich in carbonate, and frequently receive a higher amount of allochthonous nutrients from the watershed. Freshwater species assemblages may thus show affin-