Zooplankton Population Dynamics and Diaptomus Production in Waldsea Lake, a Saline Meromictic Lake in Saskatchewan

Abstract

Zooplankton population dynamics were monitored in meromictic saline Waldsea Lake, Saskatchewan, during 1974–75. The dominant zooplankton species were Diaptomus connexus, Brachionus plicatilis, Hexarthra fennica, and Daphnia similis. Diaptomus had a 1-yr life cycle. Overwintered late-stage copepodites molted into adults in May and June and were followed by sequential peaks in numbers of eggs, nauplii, and copepodites. The estimated annual production of this species was 0.6 g dry weight∙m−2 or 0.3 g C∙m−2. About 4% of the annual planktonic primary production would be required to support Diaptomus if it is 10% efficient. The standing crop of Brachionus and Hexarthra was highest in the spring and declined thereafter; Hexarthra was more abundant than Brachionus. The standing crop of Daphnia was much lower than that of either rotifer and showed a spring and fall peak in abundance. Differences in vertical distribution were present among the zooplankton species but no real vertical migrations were observed. Key words: Diaptomus connexus, zooplankton, population dynamics, production, saline meromictic lake