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Keywords:

  • Cladocera;
  • climate change;
  • Finland;
  • Holocene;
  • Lake Arapisto;
  • lake sediments;
  • palaeoclimate indicators;
  • palaeoecological methods;
  • Scandinavia;
  • species distribution

Abstract

Aim

Spatial and temporal variations in the composition of freshwater invertebrate assemblages may be useful indicators of past climate change and help us to predict species responses to future climate change. The objective of this study was to understand the relationship between climate variables and fossil Cladocera assemblages in lake sediments along a contemporary climate gradient from hemiboreal to subarctic ecoregions in Finland and throughout the Holocene climate succession.

Location

Seventy-three small shallow lakes across a climate gradient from hemiboreal (60° N) to subarctic (70° N) Finland and a case study lake, Lake Arapisto, in south boreal Finland.

Methods

Fossil cladoceran assemblages were analysed from the surface sediments of 73 lakes to investigate their association with climate, using ordination techniques (detrended correspondence analysis and redundancy analysis) and generalized linear modelling (GLM). The long-term variation of the abundance of specific climate-sensitive cladoceran species was then analysed in a sediment core from a boreal lake and compared with a chironomid-based Holocene temperature reconstruction from an adjacent lake.

Results

Mean July air temperature was identified as a significant variable in explaining species distribution across the spatial climate gradient. This result, together with GLMs that recognized several climate-sensitive species, indicates that certain cladoceran taxa may be useful indicators of climate. For example, the planktonic Bosmina longirostris and the phytophilous Graptoleberis testudinaria were more abundant in the warm southern lakes, in contrast to the benthic Alona affinis and Alona intermedia, which were typical for the cold northern lakes. The surface-sediment inferences were supported by the core analysis from Lake Arapisto, because species associated with cold lakes increased in abundance during the cold early Holocene, and species associated with warm lakes thrived during the Holocene Thermal Maximum and Anthropocene.

Main conclusions

The spatio-temporal distribution of Cladocera is regulated by regional climate, and therefore the species–climate relationships in space and time can be used to interpret past, present and future distributional patterns under a changing climate.