Gjøkvatn revisited: repeated visual observations of plankton swarms in a subarctic forest lake

Abstract

Abstract Distinct swarms of Bosmina longispina (Leydig, 1860) (Crustacea: Cladocera) were visually observed and described in Gjøkvatn, a Norwegian forest lake at 69°N, in 1969 and again in 1996 and 2021. The repeated observations after many years show that Bosmina swarms occur regularly in the lake. The swarming is likely to be an anti-predation behaviour against the predatory cladoceran Polyphemus pediculus (Linnaeus, 1761).