Liisa Nevalainen

Intra-lake heterogeneity of sedimentary cladoceran (Crustacea) assemblages forced by local hydrology

Intra-lake variation of fossil Cladocera (Crustacea) assemblages in 31 surface sediment samples in Lake Pieni-Kauro and River Saavanjoki, eastern Finland, was examined with an objective to identify habitat specificity of Cladocera in relation to local hydrology-related environmental factors. The surface sediment assemblages showed high levels of heterogeneity, mainly as to water depth and lentic–lotic gradients in the lake–river complex. This was evident from the principal component analysis which indicated a major trend from shallow to deep samples and a secondary trend from lentic to lotic samples, and from redundancy analysis (RDA), which recognized water depth and river flow as the most important environmental variables in explaining cladoceran variability within the dataset. According to the RDA and generalized linear models, Daphnia spp., Bosmina (Eubosmina), and Alona quadrangularis showed association with deep water localities, whereas Bosmina longirostris and Alona affinis preferred littoral habitats. Acroperus harpae and Chydorus sphaericus s.l. appeared to favor lotic habitats. The results propose that littoral taxa are primarily deposited postmortem or after molting close to their shallow water habitats, while planktonic cladocerans accumulate principally in deepwater locations. Accordingly, it appears that in heterogeneous basins intra-lake surface sediment samples integrate locally living fauna that is driven by local hydrology-related factors, such as water depth, sediment properties, macrophytes, and river flow and coupling biotic interactions.

Do subfossil Cladocera and chydorid ephippia disentangle Holocene climate trends

We used sedimentary records of Cladocera and chydorid (Chydoridae) ephippia to reconstruct Holocene climate trends from Lake Arapisto in southern Finland. The quantitative temperature record (TJulyCla) inferred from subfossil Cladocera was compared with a previously published pollen-based mean annual temperature reconstruction (TAnn) from the same lake. Furthermore, proportions of total chydorid ephippia (TCE), indicating proportions of asexual and sexual reproduction, were examined from the sediment core to provide supplementary data. The TJulyCla record showed a consistent trend of slowly rising July temperatures (from 12–13°C to ~15°C) during the early Holocene until ~9500 cal. BP and indicated slightly higher temperatures than prior (~16°C) during the Holocene thermal maximum (HTM) at ~7000–4000 cal. BP. The TCE record was strongly similar to the TJulyCla reconstruction during the Holocene. It suggested that chydorids would have reproduced predominantly sexually (higher TCE) under environmentally unfavorable periods (early Holocene) and some other occasions, and used mainly asexual reproduction mode under periods of stable environmental conditions (HTM). The monotony of the Cladocera-based reconstruction, when compared with the previously available pollen-based TAnn record and other reference material from the adjacent region, suggests that it was partly hampered by other forcing factors more important than temperature, such as major food-web changes or adaptation ability of cladoceran species.

LATE QUATERNARY ECOLOGICAL TURNOVER IN HIGH ARCTIC LAKE EINSTAKEN, NORDAUSTLANDET, SVALBARD (80° N)

Luoto, T.P., Nevalainen, L., Kubischta, F., Kultti, S., Knudsen, K.L. and Salonen, V.‐P., 2011: Late Quaternary ecological turnover in high arctic Lake Einstaken, Nordaustlandet, Svalbard (80° N). Geografiska Annaler: Series A, Physical Geography, 93, 337–354. DOI:10.1111/j.1468‐0459.2011.00435.x Abstract Multiproxy palaeolimnological analyses of a sediment core record from Lake Einstaken, Nordaustlandet, give insight into long‐term ecological and environmental dynamics in the High Arctic Svalbard during the last c. 13-000 cal yr bp. Fossil remains of foraminifera, chironomidae, cladocera and diatoms (Bacillariophyta) revealed several distinct ecological turnovers during the late Quaternary. The foraminiferal assemblages in a marine interval in the lower part of the core indicated one distinct faunal turnover and two subsequent minor changes. The foraminiferal assemblages reflected high‐arctic, shallow‐water conditions in an area of changing salinity conditions. A development of gradually more restricted marine conditions, presumably related to a decrease in water depth during the isostatic uplift, was evident from the foraminiferal assemblages. The Holocene was characterized by a freshwater environment in the isolated Lake Einstaken. The cladoceran assemblages experienced two complete faunal turnovers in the early part of the lacustrine sediment sequence, most likely related to inlake processes. The chironomid assemblages went through five distinct Holocene faunal changes that were probably mostly related to climate development and changes in nutrient conditions. The freshwater diatoms revealed four distinct episodes of change in their assemblages that could be related to their sensitivity to pH and nutrient status. The most distinct common feature in the Holocene faunal and floral assemblages was the pioneer phase during the early Holocene. The recent environmental changes, which were most visibly reflected in the chironomid records, are possibly related to a coupled effect of elevated nutrient conditions and increased temperatures.

Evaluation of Microcrustacean (Cladocera, Chydoridae) Biodiversity Based on Sweep Net and Surface Sediment Samples

Abstract: Biodiversity (species richness and species diversity) of chydorid Cladocera were examined by weekly sweep net sampling during the ice-free period and through surface sediment assemblages in 9 limnologically different lakes in southern Finland. Species richness in the sweep net samples was low in 2 lakes with recent ecological perturbations and the highest in one oligotrophic lake. Species diversity was the lowest in 2 eutrophicated lakes and generally higher in the oligotrophic lakes. The biodiversity values in sediment assemblages showed trends similar to those in the sweep net samples; the lowest values were observed in one of the eutrophic lakes and the highest in the oligotrophic lakes. It is likely that the observed differences were due to the impact of nutrients on the development of littoral vegetation and consequently chydorid habitats and resources. The role of nutrients as a forcing mechanism on chydorid biodiversity was indicated by high and significant negative correlations between species diversity in both total phosphorus and sweep net and sediment samples. The comparison between biodiversity in the 2 sample types showed that the biodiversity values were almost consistently higher in the surface sediment assemblages than in the sweep net samples, suggesting that surface sediment analysis provides an effective alternative method to living material examination for biodiversity evaluations.

Fossil remains of an unknown Alona species (Chydoridae, Aloninae) from a high arctic lake in Nordaustlandet (Svalbard) in relation to glaciation and Holocene environmental history

We analyzed a lacustrine sediment core covering the Holocene from Lake Einstaken, Nordaustlandet, for its fossil Cladocera (Crustacea) with an aim to reconstruct past aquatic communities in this environmentally extreme and unexplored region. In the analysis, we encountered remains (carapaces, ephippia, headshields, and postabdomens) of an unknown chydorid (Chydoridae, Aloninae) species during two separate periods in the early Holocene. The remains had some comparable morphological characters with the European Alona guttata s.str. Sars, 1862 and with the glacial relict Alona werestschagini Sinev, 1999, but they differed clearly from the previous species; the headshield had broadly rounded rostrum and narrow fornices, the ephippium was heavily pigmented and reticulated, and the postabdomen had convex dorsal and ventral margins. The postabdomen had evidently similar morphology with Alona bergi Røen, 1992, which has been described, although inadequately, from arctic Canada and northern Greenland. We conclude, based on the morphology of the postabdomen, that the unknown remains belong to species closely resembling A. bergi, named here Alona cf. bergi, and assume that the species, whether the true A. bergi or some other cryptic species of the A.guttata group, is a postglacial relict of the high arctic adapted to cold climate. Herewith, we emphasize the need for extensive biogeographical investigations into both fossil and intact specimens of chydorids in the arctic.