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Journal of the Arizona Academy of Science





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The diurnal vertical movement of zooplankton was first recorded in freshwater lakes by Weismann (1877) in Lake Constance (Bodensee), although Cuvier was credited with observing the migration of Daphniae in 1817 (Gushing, 1955). The migration is best observed in deep oligotrophic lakes and migrations of 50 m per day are described (Worthington, 1931). In addition, two species of chaetognaths are reported to migrate 400 m a day in marine waters off of Lisbon (Waterman and Berry, 1967) while Birge (1895) found little evidence of the phenomenon at all in Lake Mendota, Wisconsin.

Most zooplankton that migrate rise at night and sink during the day. Welch (1952) and Pennak (1944) point out that the most important factor involved in diurnal migration is light. It appears that the extent of the diurnal movements varies from lake to lake, among the sexes and among the age of a particular plankter. Crustaceae and some rotifers are the organisms that most often exhibit this phenomenon. Rare cases in which zooplankters show reversed migrations have been recorded (Worthington and Ricardo, 1936; Maloney and Tressler, 1942).

Previous studies on Lake Mead have dealt primarily with the physical limnology of Lake Mead (Smith, et al., 1948; National Research Council, 1949) Anderson, 1950; Anderson and Pritchard, 1951; Harbeck, et al., 1958; and Bureau of Reclamation, 1965). Moffett (1943) did a preliminary report on the plankton and fish of the lake from samples collected in November, 1941. A study by Everett (1972) showed that the highest primary productivity rates in Lake Mead occurred in the Boulder Basin. The purpose of the present investigation is to find whether nocturnal migration patterns occur in the zooplanktonic fauna of Lake Mead during times of isothermy and to determine the extent of this possible migration.


Hydrobiology; Lake Mead (Ariz. and Nev.); Phytoplankton; Zooplankton


Biochemistry | Biology | Environmental Microbiology and Microbial Ecology | Fresh Water Studies | Terrestrial and Aquatic Ecology



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