The sixth international zebra mussel and other aquatic nuisance species conference - spawned by the invasion of zebra mussels in 1986 - was held in Dearborn, Michigan in March, 1996. The conference traditionally highlights the extensive research on both ecological impact and industrial control of the zebra mussel (Dreissena polymorpha) and its close relative the quagga mussel (Dreissena bugensis).

While the focus of the research continues to be on impact and control of these damaging introductions, there is increasing recognition that there are other potentially more damaging organisms which are poised to invade North American inland waters. A number of vectors have been identified for these introductions including commercial shipping, boat or aquarium trade, authorized releases, canals, highways or railroads, and last but not least, releases through commercial seafood trade. A significant research effort has begun in an attempt to identify and prevent future releases.

Zebra and quagga mussels continue to wreak havoc on the Great Lakes ecosystem. Changes in water chemistry, as well as impacts at all levels of the aquatic ecosystem have been dramatic. Many species have been affected, in particular, native bivalves (mussels) which have been effectively eliminated in many areas. In spite of this, at least one study, by U.S. Fish and Wildlife Services, reported that young of the year perch, walleye and other fish species have not been affected. This is good news for the Great Lakes fishery which depends on these species for its viability.

The bad news is that at least one fish species contained in ballast water, the River Ruffe, which entered the Duluth area in the early 1990s, has not been contained and has now spread from Lake Superior to Lake Michigan. This fish species, which competes successfully with the yellow perch, may put new pressure on the fishery as it spreads to the lower lakes.

These mussels, removed from industrial wet well in Lake Ontario, are evidence of the molusk's prolific breeding capabilities.

In general, local mussel populations continue to fluctuate as the invasion matures. The quagga mussel now appears to be dominant in northern waters. While populations in areas of Lake Huron and Lake Ontario continue at relatively high levels, populations in Lake St. Clair and Lake Erie have dropped off somewhat and appear to be stabilized at lower levels. Numbers of larvae which were at one time detected at densities of 100,000/m3 or greater in Lake Erie are now reported consistently at 10,000 - 15,000/m3. The mussel remains a problem in the Great Lakes and has now spread throughout much of the midwestern and eastern U.S. as well as making inroads as far south as New Orleans. A handful of mussels were also detected in California on vessels, prior to launching, that were trailed overland from the east. To date no live introductions have been reported west of the Great Divide.

Research continues into control of infestation at municipal and industrial sites. A wide variety of chemical and non-chemical protocols were presented by university and private sector scientists at this conference.

Sampling ocean-going vessel ballast water in the Welland Canal to detect potential new introductions of exotic species.

For the most part, chlorine remains the chemical of choice for zebra mussel control throughout North America; however, ongoing environmental concerns as well as safety and handling issues continue to drive the research effort into alternative protocols.

Besides the use of other oxidants such as bromine or chlorine dioxide which continue to have a small following, the highest profile and most controversial control chemicals under investigation are the non-oxidizing biocides, commonly referred to as molluscicides. Researchers continue to prove the efficacy of these products. The acute toxicity of most of these chemicals, while advantageous from a treatment perspective, are problematic from an environmental impact point of view. Spills of these products may be acutely damaging, and, to date, companies that produce these products have had trouble overcoming user and regulator fears of long term toxicity and bioaccumulation in receiving water sediments. This is particularly true in Ontario where only a few experimental treatments have been approved to date.

The weight of zebra mussels removed from an industrial wet well on Lake Ontario, overwhelms a waste disposal truck, to the surprise of the operator

Other more novel chemical controls were also presented. These included the use of Endod, a natural plant extract used to control the intermediate host snail in prevention of schistosomiasis in Africa. Laboratory scale toxicity trials are in progress. In another unique trial at Wayne State University in Michigan, an antidepressant that may block or antagonize reproductive mechanisms in zebra mussels is being investigated as a means of population control.

Research on coatings was again well represented at this conference. Coatings that contained significant amounts of silicones continue to be most successful in preventing mussel settlement on concrete and steel. Three or four silicone based products were recommended; however, some problems were noted, the most important of which was the inability to apply these coatings underwater which may prevent widespread use. One novel experiment included "Penaten" cream, a product normally used by parents of newborns. This product, which has a significant zinc component, not only reduced mussel settlement but also prevented diaper rash on all of the boats tested!

There continues to be a significant effort in the area of non-chemical controls. The most promising of these appears to be the use of ultraviolet radiation. Research in this area has now moved beyond laboratory scale and installations that will treat in excess of 10,000 USGPM are planned for this coming summer. Depending on water quality it was reported that 100% mortality of zebra mussel larvae was possible using medium pressure systems which produce significant amounts of light in both UV C and UV B ranges. Other research in this area pinpointed some effective wavelengths between 250 and 290 nm. It was suggested that systems for mussel control could be available for some commercial applications by 1997/98 depending on the results in 1996.

The use of high voltage electrostatic fields and pulsed electric fields are also being investigated with mixed results. To date large scale trials have not been completed.

In another study the cathodic protection technology was shown to significantly reduce settlement on both steel and concrete structures. Full scale trials are in progress with very promising early results. This technology may rival coatings, due to ease of underwater installation, if results continue to show inhibition of mussel settlement in 1996.

All in all it appears as though a few alternative technologies are moving forward on a site or application specific basis; however, the silver bullet solution has still not shown itself. Chlorine remains the least expensive, most easily applied and most appropriate method of zebra mussel control at most sites. It remains to be seen whether new products or technologies presently being developed will alter this trend. We will apparently have to wait until the seventh annual conference to be held in New Orleans in 1997.