Ecological Effects Touted at Toronto Conference

From March 23, 1993 (Update #16)

A variety of interesting reports on the zebra mussel's ecological impacts were presented during the Third Annual International Zebra Mussel Conference Feb. 23-26 in Toronto:

* Young-of-the-year (YOY) walleye year classes in western Lake Erie were good in 1990 and 1991, but reproduction was poor during 1992, according to Ontario Ministry of Natural Resources biologist Joe Leach. YOY walleye growth showed no change over the past several years. Leach reported little post-zebra mussel change in the abundance of cladoceran and copepod zooplankton in western Lake Erie, yet he noted a great decline in the abundance of rotifers.

* The waters of Hatchery Bay in western Lake Erie are still eutrophic, though much clearer, according to University of Michigan biologist Ruth Holland. Holland has been following the abundance of diatoms - tiny silica- rich algae - before and since the invasion of zebra mussels. Although diatom numbers have declined since the invasion, she said phosphorus and nitrogen levels in the water column have remained high, and western Lake Erie waters remain eutrophic, as defined by their nutrient chemistry. Total water column phosphorus remained around 35 micrograms per liter during the mid-1980s and early 1990s, Holland said.

* Large blooms of noxious blue-green algae in Saginaw Bay and in Oneida Lake were reported, respectively, by Tom Nalepa, Great Lakes Environmental Research Lab, and Martin Horgan and Ed Mills, Cornell University Biological Field Station. Nalepa said the algal bloom in Saginaw Bay consisted primarily of Microcystis species of blue-green algae, while Horgan and Mills said the bloom in Oneida Lake consisted of Aphanizomenon species. Nalepa noted that the presence of Microcystis diminished zebra mussel filtration in mid-summer.

* Ontario water utilities continue to suffer from the effects of zebra mussels despite the implementation of control measures in water intakes, according to Mike Auger of the Ontario Ministry of the Environment. He said some of these adverse effects are due to ecological changes, such as large amounts of submerged macrophytes (commonly called "aquatic weeds") that have been drawn into municipal water intakes. Up to 1,500 pounds of these plants have entered the Windsor water intake during a single day. Frazil ice formation is another problem that has increased since the zebra mussel invasion and one that has been especially common this winter, according to Auger. He also noted that water turbidity levels in Lake Erie have dropped so low that some municipal intakes have had to add clay to assist with a flocculation process necessary for effective water treatment.

* "Quagga" mussels, a closely related form of Dreissenid mussel, may have a strong negative effect on the productivity of the deep-water Great Lakes environment, according to information presented by Ron Dermott of the Canadian Department of Fisheries & Oceans. Dermott presented results comparing benthic surveys conducted in 1979 and 1992 in eastern Lake Erie, which showed a 90 percent drop in the abundance of Diporeia (formerly called Pontoporeia), a bottom-dwelling zooplankton that is an important food source for planktivorous fish like alewives, smelt, chubs and lake herring in most offshore regions of the Great Lakes. In 1992 surveys, the quagga mussel was very abundant at sample locations. Dermott speculated that quagga mussels intercept organic material that provides food for Diporeia. In shallower areas, extra material is available for pseudofeces production, which also provides food for amphipods like Diporeia, but in deep water little extra food is available.

ID: 19930323-7.

The Zebra Mussel Update was a 4- to 8-page quarterly national newsletter published by the University of Wisconsin Sea Grant Institute from May 1990 through May 1997. The ZMU documented the spread of the zebra mussel -- an exotic nuisance mussel -- through North America's freshwater environments, especially the Great Lakes, and on efforts to control it.