Effects of fish introductions on lake ecosystems have long been debated. It has been hypothesized that such effects should be strongest in oligotrophic lakes, where fish were not originally present. We investigated two lakes (one naturally fishless, one fish-stocked in 1980) in northern Fennoscandia, selected because of the absence of other anthropogenic stressors and a well-known stocking history. The diet of the introduced brown trout (Salmo trutta L.) was analysed to estimate the effect of their predation on the pelagic invertebrate communities. Quantitative and qualitative samples were taken to assess the current abundances of pelagic macro- and micro-invertebrates in different habitats of both lakes, to infer the impact of brown trout presence. Past abundances of Cladocera, Chironomidae, Gammaruslacustris and Daphnia longispina were also estimated based on subfossil remains in the sediment, and used to assess how brown trout introduction affected macro- and micro-invertebrates living in different habitats. Relative abundance and species richness of Cladocera were evaluated in sediment cores from both lakes, to assess whether changes were caused by fish-introduction-induced trophic cascades or climate change. Also, planktonic Cladocera (Eubosmina) body sizes were measured to evaluate their response to the release of macro-invertebrate predation pressure. Brown trout introduction displaced macro-invertebrates, i.e. G. lacustris, from the pelagic area, and caused a trophic cascade effect that slightly increased the species richness of Cladocera, but markedly increased their abundance, as shown in the sediment record. Introduced brown trout did not, however, cause a decline in Chironomidae, G. lacustris or D. longispina abundances. On the contrary, it resulted in an approximately five-fold increase in Chironomidae accumulation rates in the sediment. The release of macro-invertebrate predation pressure did not lead to changes in the body shapes of Eubosmina, which could be a consequence of the composition of the original macro-invertebrate species assemblage.
The impact of trout introductions on macro- and micro-invertebrate communities of fishless boreal lakes
Milardi, Marco;
2016
Abstract
Effects of fish introductions on lake ecosystems have long been debated. It has been hypothesized that such effects should be strongest in oligotrophic lakes, where fish were not originally present. We investigated two lakes (one naturally fishless, one fish-stocked in 1980) in northern Fennoscandia, selected because of the absence of other anthropogenic stressors and a well-known stocking history. The diet of the introduced brown trout (Salmo trutta L.) was analysed to estimate the effect of their predation on the pelagic invertebrate communities. Quantitative and qualitative samples were taken to assess the current abundances of pelagic macro- and micro-invertebrates in different habitats of both lakes, to infer the impact of brown trout presence. Past abundances of Cladocera, Chironomidae, Gammaruslacustris and Daphnia longispina were also estimated based on subfossil remains in the sediment, and used to assess how brown trout introduction affected macro- and micro-invertebrates living in different habitats. Relative abundance and species richness of Cladocera were evaluated in sediment cores from both lakes, to assess whether changes were caused by fish-introduction-induced trophic cascades or climate change. Also, planktonic Cladocera (Eubosmina) body sizes were measured to evaluate their response to the release of macro-invertebrate predation pressure. Brown trout introduction displaced macro-invertebrates, i.e. G. lacustris, from the pelagic area, and caused a trophic cascade effect that slightly increased the species richness of Cladocera, but markedly increased their abundance, as shown in the sediment record. Introduced brown trout did not, however, cause a decline in Chironomidae, G. lacustris or D. longispina abundances. On the contrary, it resulted in an approximately five-fold increase in Chironomidae accumulation rates in the sediment. The release of macro-invertebrate predation pressure did not lead to changes in the body shapes of Eubosmina, which could be a consequence of the composition of the original macro-invertebrate species assemblage.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
