[Date Prev][Date Next][Date Index]
Environmentally Sensitive Organisms Missing in Lake Michigan Mud Samples
- Subject: Environmentally Sensitive Organisms Missing in Lake Michigan Mud Samples
- From: firstname.lastname@example.org (Michael A. Quigley)
- Date: Wed, 3 Dec 1997 14:31:52 -0500
- List-Name: GLIN-Announce
U.S. Department of Commerce
National Oceanic and Atmospheric Administration
EMBARGOED FOR RELEASE UNTIL 11 a.m. Dec. 4
Contact: Dane Konop Mike Quigley (GLERL)
(301) 713-2483 (313) 741-2149
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 NOAA'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
"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 5-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 then eventually settle to the lake bottom. Amphipods then
would readily feed and grow on this plant material. NOAA studies have shown
that when amphipods feed on this rich material, their lipid (fat) content
goes way up. 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:
All NOAA press releases and links to other NOAA material can be found on the
Internet at http://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 email@example.com, or fax to