Abstract
The life cycles of Cyclops scutifer Sars (Copepoda, Crustacea) in two high mountain lakes in Norway, Gjende and Bessvatn in Jotunheimen, are presented. The population in Gjende has an exclusive 2‐yr life cycle and that in Bessvatn a 3‐yr cycle which is exceptionally long both among freshwater and marine zooplankton. Bessvatn is situated about 400 m higher than Gjende, and the heat preservation is lower with longer periods of ice cover and lower primary production explaining the difference in cycle length. The prolongation of the life cycle is due mainly to retardation of the developmental rate during the long periods of winter stagnation with water temperatures mostly below 2°C. The retardation is especially evident in the nauplii and in the copepodid instars III, IV, and V. Neither population diapauses. Reproduction takes place only in late summer and no adults survive the winter.
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