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Department of Biological Sciences: University of Nevada, Las Vegas


Microfaunal communities were studied in littoral (inshore) and limnetic (offshore) areas of the lower basin in Lake Mead to compare species composition and abundance between the two zones. Planktonic forms (zooplankton) dominated inshore and offshore habitats and the occurrence of littoral species was low. Therefore, high similarity in zooplankton species composition was found among all sampling stations. This was perhaps due to two main factors: (i) the physical and chemical environment among the stations were very similar and (ii) the lack of aquatic vegetation in the littoral zone reduced the occurrence of littoral species.

Although species composition did not vary a great deal, there were large differences in average zooplankton densities between sampling stations. This was most likely due to differences in the amount of algal biomass and fish predation. The more productive station in inner Las Vegas Bay showed a higher relative algal biomass and a higher average density of zooplankton (about 118.1-1) than other sampling stations. In middle Las Vegas Bay, average zooplankton densities (44.1-1 in the limnetic zone and 80.1-1 in the littoral zone) and relative algal biomass were less than inner Las Vegas Bay. Boulder Basin had the lowest relative algal biomass and, therefore, lowest average zooplankton densities (about 23.1-1 in the limnetic zone and 37.1-1 in the littoral zone) of any location.

Relative abundance of fish increased at sampling areas in late spring and summer when fishes migrated from deeper areas of the reservoir to the surface waters to spawn. Adult planktivorous fishes and newly hatched young then decimated zooplankton populations causing low summer zooplankton densities. Fish predation was more intense in inner Las Vegas Bay and middle Las Vegas Bay and less in Boulder Basin. Fish predation was also greater in littoral areas than limnetic areas.


Algae; Freshwater fishes; Lake Mead (Ariz. and Nev.); Limnetic zone; Littoral zone; Zooplankton


Biology | Environmental Indicators and Impact Assessment | Environmental Monitoring | Fresh Water Studies | Natural Resources and Conservation | Terrestrial and Aquatic Ecology | Water Resource Management