Restoration of zooplankton in a small acidified mountain lake (Plešné Lake, Bohemian Forest) by reintroduction of key species

Atmospheric acidification brought about the extinction of several species of planktonic Crustacea in lakes of the Bohemian Forest (Sumava, Bohmerwald). The recent reversal in chemical parameters of lake water towards pre-acidification values raises the question whether the return of missing species is possible. We have designed a bioassay to test water from different lakes for the survival of Daphnia longispina, which inhabited the lakes under study but disappeared from those most affected by acidification. The bioassay showed the best survival in water from Plesne Lake, one of those where Daphnia and Cyclops became extinct. A large-scale experiment was conducted by transplanting Daphnia longispina (Crustacea, Cladocera) and Cyclops abyssorum (Crustacea, Copepoda) from Prasilske Lake, where they have survived until the present, to Plesne Lake. One year later, a successful reintroduction was confirmed for Cyclops abyssorum.