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GLIN==> Burrowing Mayflies: BRD News Release



     
     U.S. Department of the Interior            
     U.S. Geological Survey             
     
     
     Release  Date: July 13, 1999
     
     John Gannon  Phone:734-214-7237  Fax: 734-214-7201 E-mail: 
     john_gannon@usgs.gov
     
     Catherine Haecker  Phone:703-648-4283  Fax: 703-648-4042 E-mail: 
     catherine_haecker@usgs.gov
     
     
     Burrowing Mayfly Swarms Signal a Healthier Ecosystem, USGS Scientists 
     Say 
     
     While swarms of flying insects may have little appeal for most people, 
     USGS biologist Thomas Edsall says the clouds of burrowing mayflies 
     emerging from western Lake Erie this summer are a welcome sign of an 
     ecosystem in recovery. 
     
     "They're telling us that the water's clean out there," Edsall says.
     
     Burrowing mayflies are large aquatic insects that spend most of their 
     lives -- about two years -- in their larval form, living in shallow 
     bottom sediments of lakes. On the bottom of western Lake Erie, larval 
     mayflies -- known as nymphs -- once numbered dozens per square foot, 
     and occasionally even reached numbers as high as a 100 per square 
     foot. But populations decreased dramatically in the 1950s due to 
     deteriorating water quality, and throughout most of the next three 
     decades burrowing mayflies were virtually absent from their former 
     Great Lakes habitat.
     
     For the last five years, however, a remarkable recovery has been 
     underway.  Edsall and his colleagues at the USGS Great Lakes Science 
     Center report that nymphs in western Lake Erie have increased from 
     near zero to numbers approaching those of the early twentieth century.
     
     Edsall says the mayfly recovery is a strong sign that improvements in 
     water quality, which have been taking place since the 1970s, have 
     resulted in a healthier, more normally functioning ecosystem. "This is 
     a real tribute to the EPA's enforcement of water pollution control 
     laws, such as the Clean Water Act and U.S. and Canadian cooperation 
     through the Great Lakes Quality Agreement," he says.
     
     USGS and Canadian biologists have used several different methods to 
     determine the past distribution and abundance of burrowing mayflies in 
     Lake Erie and to understand how the insects have responded to 
     different forms of water and sediment of contamination. Sediment core 
     samples, dating back to about 1740, contain jaw parts and other 
     preserved remains that provide a continuous record of burrowing mayfly 
     densities in different regions of the lake. Other information comes 
     from periodic sampling of nymph populations, which began in 1930, and 
     from records of the incidence of mayflies in fish stomachs.
     
     In the western-most end of the lake, USGS biologists Bruce Manny and 
     Donald Schloesser have found that contamination of bottom sediments by 
     oil and metals was the main factor in eliminating burrowing mayfly 
     populations. New clean water standards have greatly reduced the amount 
     of such contaminants released into the lake. Meanwhile the steady, 
     natural accumulation of lake sediments has finally buried the toxins 
     lining the lake bottom a few decades ago, creating a habitat that is 
     again suitable burrowing mayflies.
     
     Edsall says the massive declines of the 1950s were brought about by a 
     combination of factors. Deep-water areas in central Lake Erie became 
     periodically depleted of oxygen due to the decomposition of algae that 
     had accumulated as a result of sewage and fertilizers entering the 
     lake. This oxygen-deprived water sometimes moved into adjacent shallow 
     areas occupied by nymphs, causing mass die-offs.
     
     The recovery of this one species may be good news for the entire Lake 
     Erie ecosystem, says Edsall. Burrowing mayflies play an important role 
     in maintaining the transfer of energy and nutrients across different 
     levels of aquatic food webs, and their burrowing activity re-suspends 
     buried nutrients into the water, which fuels the growth of aquatic 
     plants. Nymphs feed on decaying plant matter, and both nymphs and 
     flying adults are preyed upon by various species of fish, including 
     species such as yellow perch that are important in commercial and 
     recreational fisheries.
     
     "From a fisheries perspective, burrowing mayflies are really important 
     because they're a huge food resource," says Edsall. "They have a high 
     energy content, which makes them prime fish food."
     
     Even though the insects are only available in large numbers during the 
     two- to three-week period each year when nymphs rise to the surface and 
     hatch into winged adults, this brief super-abundance of food can make a 
     critical difference in determining whether or not fish grow and 
     reproduce. Yellow perch in Lake Erie have been in low abundance since 
     the 1950s, when the burrowing mayfly population declined. Edsall is 
     hopeful that the mayfly recovery will spark a similar recovery in the 
     perch population.
     
     Edsall acknowledges that for a few weeks every summer the burrowing 
     mayfly hatch can be a nuisance for boaters and lakeshore residents, 
     and that the mayflies make fishing a hopeless endeavor. But that may 
     be a small price to pay for a cleaner, healthier lake environment.
     
     As the nation's largest water, earth and biological science and 
     civilian mapping agency, the USGS works in cooperation with more than 
     2000 organizations across the country to provide reliable, impartial, 
     scientific information to resource managers, planners, and other 
     customers. This information is gathered in every state by USGS 
     scientists to minimize the loss of life and property from natural 
     disasters, contribute to the sound conservation, economic and physical 
     development of the nation's natural resources, and enhance the quality 
     of life by monitoring water, biological, energy and mineral resources. 
     
                                                        ###USGS###
     
     
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