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GLERL What's New 1997
NOAA Office of Public
Affairs
National Oceanic and Atmospheric Administration
U. S. Department of Commerce
1997 PRESS RELEASE
Contact: Dane Konop Mike Quigley (GLERL)
(301) 713-2483 (313) 741-2149
dane.konop@noaa.gov michael.a.quigley@noaa.gov
ENVIRONMENTALLY SENSITIVE ORGANISMS MISSING IN LAKE MICHIGAN MUD SAMPLES
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 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: 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 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 releases@www.rdc.noaa.gov, or fax to (202) 482-3154.
Last Update: September 3, 2002 mbl