Abstract
Lakes in the Alps represent a considerable fraction of nutrient-poor lakes in Central Europe, with unique biodiversity and ecosystem properties. Although some individual lakes are well studied, less knowledge is available on large-scale patterns essential to general understanding of their functioning. Here, we aimed to describe crustacean zooplankton communities (Cladocera, Copepoda) and identify their environmental drivers in the pelagic zone of 54 oligotrophic lakes in the montane region of the Alps (400–1200 m) in Austria, Germany, and Switzerland, covering a spatial scale of 650 km. Moreover, we aimed to provide data on the distribution and ecological requirements of the North American invader Bythotrephes longimanus in its Central European native range. Communities were mainly dominated by widespread species typical of lowland habitats, and only a few true specialists of oligotrophic alpine lakes were present. The most frequent taxa were the Daphnia longispina complex and Eudiaptomus gracilis, with 48 and 45 occurrences, respectively. Species richness decreased with altitude and increased with lake area. The main structuring factors of community composition were chlorophyll a concentration and depth, which drove an apparent separation of mesotrophic and oligotrophic communities. Bythotrephes had 13 occurrences, showing a preference for deep oligotrophic lakes. Its presence was not coupled with lower crustacean species richness, as was repeatedly observed in North America. Additionally, it frequently co-occurred with the other large predatory cladoceran, Leptodora kindtii. B. longimanus might be considered a truly montane species in Central Europe, given its absence in lowland and alpine lakes.
Highlights
In oligotrophic lakes, nutrients are the primary limiting factor for biomass production
In addition to the lakes visited during our survey, we found 14 instances in the literature where Bythotrephes has been reported in the Alps within the last 30 years (Fig. 1; Appendix 7), mostly in the vicinity of Austrian or Swiss lakes involved in our analyses, with an additional group of lakes in the Italian Alps
Trophic state indicated by chlorophyll a (Chl-a) and total phosphorus (TP) decreased with increasing elevation in our dataset, these relationships were not significant, neither in the whole dataset (Appendix 2) nor in the subset of Austrian and German lakes (Appendix 6)
Summary
Nutrients are the primary limiting factor for biomass production. Plankton communities are relatively simple and species-poor, yet zooplankton– phytoplankton interactions are stronger than in eutrophic lakes (McQueen et al 1986), and plankton in general plays a central role in ecosystem functioning (Straškrabová et al 1999, Callieri et al 2002, Sarnelle and Knapp 2005) Compared to their boreal counterparts (Rühland et al 2003, Lepistö et al 2004, Hessen et al 2006, Walseng et al 2006, Ptacnik et al 2008, 2010), little is known about regional patterns of plankton diversity in alpine lakes (Anderson 1971, Knapp et al 2001, Reche et al 2005, Tolotti et al 2006), mostly due to the remoteness and low accessibility of lakes in mountainous areas (Straškrabová et al 1999, Sommaruga 2001). Aquatic habitats in mountainous areas are especially perceptive to changes in both precipitation and temperature regimes (Sommaruga-Wögrath et al 1997, Sommaruga et al 1999), which can induce significant changes in the biomass and composition of plankton communities of these lakes (e.g., Sommaruga et al 1999, Holzapfel and Vinebrooke 2005, Shatwell et al 2008)
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