Cladocera Remains From The Sediments Of Remote Cold Lakes: A Study Of 294 Lakes Across Europe

Sediment cores were taken from 294 lakes in 12 different remote Mountain areas in Europe (from Greenland to Finland in the north and from Spain to Bulgaria in the south) for the analyses of Cladocera remains. Surface samples (0 - 0.5 cm) were analysed to examine the contemporary distribution of Cladocera. These were compared with sub-samples from the pre-industrial period (depth > 15 cm) to assess changes in species composition over time. In total, the remains of 42 different Cladocera taxa were identified tied in the surface sediments. The number of taxa per lake decreased from north to South, which also corresponded to a gradient of increasing altitude. On average, 12 taxa per lake were found in northern regions (Scotland, North Finland = high-latitude lakes) and ca. 4 taxa in the southern regions (Romania, Bulgaria, Slovenia, Austria = high-altitude lakes). The most common taxa, occurring in the majority of lakes, were Alona affinis, Chydorus sphaericus, Daphnia longispina gr., Alona quadrangularis and Acroperus harpae. Most other species were also widely distributed across several of the lake districts, suggesting that all cold water lakes in Europe are equally favourable habitats for cladocerans. Eurycercus glacialis and Eubosmina longispina were the most abundant species restricted to specific regions, the former to Greenland and the latter to Northern Finland. Multivariate statistical analyses showed that the taxa assemblages were primarily determined by biogeographical factors. Dispersal limitations at high altitudes may be the most important factor for the differences in species diversity among districts. Physical, chemical and trophic conditions appeared to explain little of the variation independent of geographical location, though the potential role of fish predation is discussed. Comparisons between the top and the bottom section of the sediment cores revealed similar taxa numbers, but most cores, although only marginally, differed in taxa assemblage.