Chydoid ephippia as indicators of environmental change biostratigraphical evidence from two lakes in southern Finland

Abstract

This study presents a new proxy method for studying past environmental change. The method is based on the relative abundance of ephippia of chydorid Cladocera (Chydoridae). Ephippia are a modification of the carapace that protects the resting eggs against, for example, freezing and desiccation. Holocene records of chydorid ephippia and other gamogenetic remains (male headshields and postabdomens, and headshields of ephippial females) from two lakes in southern Finland (Rutikka and Kaksoislammi) are presented. Results of pollen, diatom and cladoceran analyses from Rutikka Lake are also described. Results from this study suggest that chydorid ephippia are valuable indicators of the environmental stresses occurring in lakes. In particular, ephippia were abundant at both sites during the late Pleistocene/early Holocene transition when the climate was still severe and the open-water season was short. In the later-Holocene record, the relative abundance of the ephippia also reflected the environmental stress during profound changes in predator-prey relationships in Kaksoislammi Lake. In contrast, a change in the relative abundance of ephippia of only one species (Alona affinis) occurred in the late Holocene in Rutikka Lake when prehistoric cultivation took place and affected the water chemistry.