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"Norman Dennis Edelen, Jr." <normane at hevanet_com>: NANFA-- Fw: Fwd:Amphipods missing from Lake Michigan mud samples
Here is an interesting item I received from a friend.
> ENVIRONMENTALLY SENSITIVE ORGANISMS MISSING IN LAKE MICHIGAN MUD
> Tiny shrimp-like animals called amphipods that are normally found in
> muds of healthy lakes were absent in samples taken in November at a
> site on southern Lake Michigan, according to the National Oceanic and
> Atmospheric Adminstration's Great Lakes Environmental Research
> Ann Arbor, Mich.
> Routine monitoring of the abundance of these environmentally sensitive
> organisms at forty sites in Lake Michigan's southern basin provides
> researchers with a reliable measure of the lake's health. While NOAA
> scientists have not yet determined the exact cause of the disappearance
> amphipods at the site five miles off St. Joseph, Mich., they suspect it
> linked to the introduction of zebra mussels in southern Lake Michigan
> severely limiting food available to the amphipods.
> Since amphipods normally make up to 70 percent of the living biomass in
> given area of healthy lake bottom, their decline in Lake Michigan may
> hard times for a variety of fish species that depend heavily on them
> according to Great Lakes Environmental Research Laboratory biologist
> Nalepa, who has been sampling Lake Michigan sediments since the early
> "What's happening is energy that used to support amphipod growth is now
> turned into zebra mussel tissue," says Nalepa. "Many species of fish,
> particularly young fish, readily eat amphipods, but few species can use
> mussels for food. There's concern that such a short circuit in the food
> could lead to declines in a number of fish, including perch, alewives,
> sculpin, bloater and smelt, with possible secondary effects on trout
> salmon predators."
> Data collected in the early 1990's indicated that the declines have
> concentrated over a five-mile-wide strip of lake bottom extending along
> eastern Lake Michigan shore from near Chicago at the southern end to
> "Although amphipod populations declined by 60 to 90 percent in the
> 1990's, there were still at least some of these animals left. When we
> through samples from the St. Joseph site in early November, we couldn't
> single amphipod. We just couldn't believe it," Nalepa said.
> "During the 1980's, that site had 9,600 amphipods living on every
> of lake bottom," Nalepa said. "Now, they're all gone. We're now
> about how extensive this dead area might be. We hope that additional
> planned for 1998 can provide the answers."
> To sample the lake bottom, Nalepa uses a device called a "Ponar grab,"
> shovel-like device that is lowered by cable to the lake bottom from the
> research vessel Shenehon to retrieve a measured scoop of mud. Once
> ship, the sample is then washed through a fine sieve to strain out any
> living in the mud.
> While other organisms are still present in the mud, they are not as
> fed upon by fish as are amphipods. Prior to the zebra mussel's
> Lake Michigan, amphipods had relied on a rich crop of microscopic
> called diatoms for growth and survival. Diatoms bloom in lake waters in
> spring and eventually settle to the lake bottom, where Amphipods
> and grow on this plant material. NOAA studies have shown that when
> feed on this rich material, their lipid (fat) content increases. That
> energy is what fuels their growth and survival through the remaining
> Large concentrations of zebra mussels residing on rocky bottom areas of
> southern Lake Michigan may be filtering out diatoms and thereby
> to amphipods, according to Nalepa.
> # # #
> NOTE TO EDITORS: The Great Lakes Environmental Research Laboratory,
> 2205 Commonwealth Blvd. in Ann Arbor, will hold a press briefing by Dr.
> on these findings at 10 a.m., Thursday, December 4.
> A map of amphipod abundance in southern Lake Michigan during the 1980's
> can be found at: http://www.glerl.noaa.gov/pubs/PandP/9697/tfn97-4.html
> [Note: hit "Page Down" twice to view graphic.] A photo of an amphipod
> found at: http://www.epa.gov/glnpo/image/57.jpg .
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