Substratum associations and depth distribution of benthic invertebrates in saline Walker Lake, Nevada, USA
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Walker Lake, a terminal salt lake in western Nevada, is undergoing rapid changes because of falling lake level and rising salinity, affecting the potential habitat of benthic invertebrates that supply food to native fish and birds. Benthic invertebrate surveys were conducted within different substratum size classes and macrophyte beds in the nearshore littoral shallows (<1 m) and in the deeper offshore littoral (2–10 m) and profundal (>10 m) zones of the lake. Samples were dominated by the chironomid midges Cricotopus ornatus and Tanypus grodhausi; the damselfly Enallagma clausum; and an oligochaete worm of the genus Monopylephorus. Midges showed distinct depth preferences, with Cricotopus found primarily in the shallow littoral, and Tanypus found in the lower littoral and profundal regions. Enallagma occurred throughout the littoral region but was reduced in abundance below 10 m. Cricotopus and Enallagma were most abundant on cobble rock substratum and macrophytes. Sand and small gravel substrata supported few invertebrates except oligochaetes, which were most common in shallow littoral areas. The extent of Ruppia beds was determined using hydroacoustic sounding and showed that these beds were most well-developed in a zone from 1.25 to 5 m depth. The estimated area of productive shallow littoral zone habitat at different lake levels showed that coverage was lowest near the current surface elevation. Rising lake levels would result in expansion of suitable habitat area, and while falling levels could also expand nearshore habitat, this would likely occur on areas of poorer substratum quality and under high salinities that may inhibit growth.
KeywordsWalker Lake Saline lakes Substratum preference Depth distribution Lentic benthos Benthic invertebrates Littoral zone
We thank the Lahontan National Fish Hatchery Complex of the United States Fish and Wildlife Service for funding this study (Agreement #81332-5-G004, Desert Terminal Lakes Program), and the advice and oversight of Lisa Heki and Stephanie Byers. Kim Rose provided assistance with boat-based sampling, and laboratory facilities were provided by the Sierra Nevada Aquatic Research Laboratory of University of California’s Natural Reserve System. Thanks also to Steve Fend for identification of saline lake oligochaetes. Recognition should also be given to Senator Harry Reid for his championing of the plight of the rare saline desert lakes of Nevada. Comments of anonymous reviewers have been helpful in improvements of the paper.
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