Document Type


Publication Date



University of Nevada, Las Vegas


Zooplankton samples collected from throughout Lake Mead, in 1981-1982, demonstrate the presence of a statistically significant seasonal and spatial heterogeneity in zooplankton densities. Seasonally, the major zooplankton groups were most abundant in the spring and fall, coincident with maxima in chlorophyll-a concentrations. Successions among the various rotifers, cladocerans and copepods present in the reservoir were influenced by food availability, diapause, predation by planktivorous fish and, possibly, water temperatures.

Spatial heterogeneity in zooplankton densities was unrelated to water temperature, pH, conductivity and dissolved oxygen concentrations, but was related to the abundance of phytoplankton (chlorophyll-a concentrations) and fish. Statistical analyses indicate that a direct relationship between phytoplankton and zooplankton standing crops exists in Lake Mead. This relationship is clearly evident in the coincidence of seasonal and spatial maxima of chlorophyll-a concentrations and zooplankton densities. Comparison of the results of this study with other studies on Lake Mead zooplankton indicate that since 1971, the density of zooplankton in limnetic areas has declined by over 90%. This decline parallels decreases in chlorophyll-a concentrations which have occurred during this same period.


Aquatic ecology; Chlorophyll; Environmental quality; Freshwater fishes; Lake Mead National Recreation Area (Ariz. and Nev.); Limnology; Plankton; Phytoplankton; Zooplankton


Aquaculture and Fisheries | Biology | Environmental Health and Protection | Environmental Indicators and Impact Assessment | Environmental Monitoring | Fresh Water Studies | Life Sciences | Microbiology | Natural Resources Management and Policy | Sustainability | Terrestrial and Aquatic Ecology