FOR IMMEDIATE RELEASE Dane Konop Michael Quigley
In a just-published series of scientific papers, university researchers and scientists from the Great Lakes Environmental Research Laboratory in Ann Arbor, Mich., have documented basic changes in the food chain in zebra mussel-infested waters of Lake Huron's Saginaw Bay that threaten water quality and healthy fisheries across the Great Lakes ecosystem. The lab is run by the Commerce Department's National Oceanic and Atmospheric Administration.
In general, the research shows an alarming shift in how energy and nutrients are routed through the food chain. Results show that Saginaw Bay's energy base is no longer dominated by phytoplankton because these microscopic, free-floating plant cells are choice food for zebra mussels, which are able to selectively filter the cells out of the water.
The spread and growth of zebra mussels have decimated this important free-floating part of the food chain, raising concerns that all of the bay's fish stocks may suffer.
Zebra mussels are also encouraging growth of harmful blue-green algae by rejecting them as food, thus giving them a competitive advantage over less abundant algae that are eaten by the mussels. The mussels may also release nutrients that encourage algae growth, especially blue-green algae.
This in addition to a sudden change from a free-floating to a bottom-dominated food base may force scientists and decision- makers to reassess current models used to guide the management of water quality, fisheries and toxic contaminants throughout the Great Lakes region.
Saginaw Bay was studied because it serves as a ready-made laboratory large enough to reflect changes expected for a whole lake, but small enough to allow scientists to sample everything up and down the ecosystem food chain. Also, there was already much information available on the bay--a water body with a rich fishery made possible by the high biological production of its microscopic phytoplankton and zooplankton.
Zebra mussels were found capable of filtering Saginaw Bay's entire water volume in one to four days. While this high filtering rate fuels explosive zebra mussel growth, it also means that other parts of the food chain are deprived of needed energy and nutrients. Prior to the zebra mussel's arrival, much of this energy and nutrients supported microscopic animals (zooplankton) that in turn served as a food base for young (larval) fish. The spread and growth of zebra mussels have decimated this important free-floating part of the food chain, raising concerns that all of the bay's fish stocks may suffer.
Mussels may also release nutrients that encourage algae growth, especially blue-green algae. Certain forms of a blue-green algae named Microcystis are toxic to fish and cause gastro-intestinal distress in humans. Blooms of Microcystis have recently been noted in Saginaw Bay and in western Lake Erie, where studies are underway. With increased water clarity due to the mussel's continued filtering of the bay's water, thick mats of thread-like algae now are abundant near and on some water intakes. These algae have the capability of producing off-flavor compounds that can affect taste and odor of municipal water supplies.
The zebra mussel has transformed the Saginaw Bay ecosystem from one that scientists understood fairly well, to a new system with a large number of unknowns. Additional work will be needed to document and fully understand how this new system behaves.
Although a certain amount of change has and will continue to occur in the structure and function of Great Lakes ecological systems, NOAA and university scientists emphasized that the zebra-mussel-induced changes they have seen in Saginaw Bay's ecology are more extreme because it is shallow and has suitable substrate for the mussels. In the long run, more ecological instability can be expected wherever zebra mussels spread, making the ecosystem more difficult to predict and, therefore, more difficult to manage and protect vital resources.
In addition to the yet-unknown economic impacts on Great Lakes fisheries, costs to reverse or prevent zebra mussel fouling in water plants and other industrial water works alone are estimated to total $5 billion by the year 2000.