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"Norman Dennis Edelen, Jr." <normane at hevanet_com>: NANFA-- Fw: Fwd:Amphipods missing from Lake Michigan mud samples




Hello All,

Here is an interesting item I received from a friend.

Norm

>
>   ENVIRONMENTALLY SENSITIVE ORGANISMS MISSING IN LAKE MICHIGAN MUD
SAMPLES
>
> Tiny shrimp-like animals called amphipods that are normally found in
bottom
> muds of healthy lakes were absent in samples taken in November at a
monitoring
> site on southern Lake Michigan, according to the National Oceanic and
> Atmospheric Adminstration's Great Lakes Environmental Research
Laboratory
in
> 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
of
> amphipods at the site five miles off St. Joseph, Mich., they suspect it
is
> linked to the introduction of zebra mussels in southern Lake Michigan
in
1989,
> severely limiting food available to the amphipods.
>
> Since amphipods normally make up to 70 percent of the living biomass in
a
> given area of healthy lake bottom, their decline in Lake Michigan may
spell
> hard times for a variety of fish species that depend heavily on them
for
food,
> according to Great Lakes Environmental Research Laboratory biologist
Tom
> Nalepa, who has been sampling Lake Michigan sediments since the early
1980's.
>
> "What's happening is energy that used to support amphipod growth is now
being
> turned into zebra mussel tissue," says Nalepa. "Many species of fish,
and
> particularly young fish, readily eat amphipods, but few species can use
zebra
> mussels for food. There's concern that such a short circuit in the food
chain
> could lead to declines in a number of fish, including perch, alewives,
> sculpin, bloater and smelt, with possible secondary effects on trout
and
> salmon predators."
>
> Data collected in the early 1990's indicated that the declines have
been
> concentrated over a five-mile-wide strip of lake bottom extending along
the
> eastern Lake Michigan shore from near Chicago at the southern end to
St.
> Joseph.
>
> "Although amphipod populations declined by 60 to 90 percent in the
early
> 1990's, there were still at least some of these animals left. When we
picked
> through samples from the St. Joseph site in early November, we couldn't
find a
> single amphipod. We just couldn't believe it," Nalepa said.
>
> "During the 1980's, that site had 9,600 amphipods living on every
square
meter
> of lake bottom," Nalepa said. "Now, they're all gone. We're now
wondering
> about how extensive this dead area might be. We hope that additional
sampling
> planned for 1998 can provide the answers."
>
> To sample the lake bottom, Nalepa uses a device called a "Ponar grab,"
a
steel
> shovel-like device that is lowered by cable to the lake bottom from the
lab's
> research vessel Shenehon to retrieve a measured scoop of mud. Once
aboard
the
> ship, the sample is then washed through a fine sieve to strain out any
animals
> living in the mud.
>
> While other organisms are still present in the mud, they are not as
readily
> fed upon by fish as are amphipods. Prior to the zebra mussel's
appearance
in
> Lake Michigan, amphipods had relied on a rich crop of microscopic
plants
> called diatoms for growth and survival. Diatoms bloom in lake waters in
early
> spring and eventually settle to the lake bottom, where Amphipods
readily
feed
> and grow on this plant material. NOAA studies have shown that when
amphipods
> feed on this rich material, their lipid (fat) content increases. That
stored
> energy is what fuels their growth and survival through the remaining
year.
> Large concentrations of zebra mussels residing on rocky bottom areas of
> southern Lake Michigan may be filtering out diatoms and thereby
depriving
food
> to amphipods, according to Nalepa.
>
>                                     # # #
>
> NOTE TO EDITORS: The Great Lakes Environmental Research Laboratory,
located at
> 2205 Commonwealth Blvd. in Ann Arbor, will hold a press briefing by Dr.
Nalepa
> on these findings at 10 a.m., Thursday, December 4.
>
> A map of amphipod abundance in southern Lake Michigan during the 1980's
-
90'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
can
be
> found at: http://www.epa.gov/glnpo/image/57.jpg .
>
> All NOAA press releases and links to other NOAA material can be found
on
the
> Internet at www.noaa.gov/public-affairs . Journalists who wish to be
added
to
> NOAA's press release distribution list, or who wish to switch from fax
to
> e-mail, can send an e-mail to releases at www_rdc.noaa.gov , or fax to
(202)
> 482-3154.
>
>
>
>
>