Periodicity of Crustaceans in a Saline Prairie Stream of Alberta, Canada

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Abstract
Sounding Creek is a moderately saline prairie stream located in east-central Alberta, Canada. Total drainage area at the study site is 6600 km2; the basin is endorheic, and extensive areas of the stream dry up each summer. The stream supports a diverse crustacean fauna, 60 spp. having been identified; and about 1/2 of these were abundant at some time during the 2 yr (1972-1973) that the stream was regularly sampled. Phyllopods (Anostraca and Conchostraca) were especially abundant. The fairy shrimp (Eubranchipus ornatus) exhibited a rapid life cycle, being present for only 1 mo. after the ice melted in April. E. bundyi and E. intricatus populations required about 2 mo. (April-early June) to complete their life cycles. Sexually mature E. bundyi specimens were present for about 10 days, whereas sexually mature E. intricatus specimens were present for about 20 days. The conchostracans Lynceus brachyurus and L. mucronatus were found in large numbers. The L. mucronatus population completes its life cycle in about 60 days, which is about 1/2 the time required by L. brachyurus. Adult males and ovigerous females of Cyzicus mexicanus, another conchostracan, persisted throughout the summer. Life cycle observations are also presented for the abundant cladocerans, copepods, ostracods and the amphipods Hyalella azteca and Gammarus lacustris. An absence of predators may not be necessarily essential for phyllopod success, since both anostracans and conchostracans coexist for at least part of the year with potential predators (e.g., beetle larvae, odonate nymphs, fathead minnows) in Sounding Creek. In some cases C. mexicanus and Lepidurus couesii exist for a longer period of time each year than most of the other inhabitants of the stream.

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