Consultant's Report - Minnesota State Legislature

MINNESOTA DEPARTMENT OF NATURAL RESOURCES
Feasibility Study to Limit the Spread of Zebra Mussels from Ossawinnamal{ee Lake
Zebra mussels are sensitive to a number of enviromnental factors that can be manipulated to
induce mortality of various life stages. Aerial exposure, calcium deficiency, acute or chronic
heat exposure, oxygen deprivation, parasitism, predation, and starvation are all natural control
methods that could potentially reduce the size ofzebra mussel populations. There is potential for
increasing the salinity or decreasing the calcium concentration of the infested enviromnent
without major enviromnental impacts, but parameters such as dissolved oxygen, pH, and
temperature are difficult to manipulate at levels that would affect zebra mussels. In addition,
most of these factors cannot be manipulated in an open water system without serious
repercussions. Since these biological and physiological control methods have been discussed in
the previous section, they will not be discussed in great detail here. Please refer to Table IV-2
(Resistance Adaptation of Zebra Mussels to Physio-Chemical Parameters) in Section IV for an
overview of these tolerances. Bacterial exposure and inhibition of spawning are additional
biological treatments that could potentially be implemented in an open water system. These
biological control methods are well documented, but they have not been widely implemented.
Bacterial Exposure
Research findings by Molloy (1998) have shown that a natural bacterial toxin found in the
CL0145A strain of Pseudomonas fluorescens is lethal to zebra muss,els by destroying the
mussel's digestive tract (Molloy 2001). Molloy also found that alive and dead bacterial cells
were equally effective against the zebra mussel, suggesting that the biotoxin is likely found in the
cell walls of the bacterium. Unlike some biocides and other chemical treatment methods, the
ingestion of CL0145A did not elicit an immediate adverse response in zebra mussels (i.e.,
closing off siphons to adverse conditions). Therefore, it is likely that fewer and shorter
treatments would likely be required with CL0145A. All zebra mussel sizes (1 to 25 mm shell
length) appeared to be equally susceptible to CL0145A, and unlike other treatment technologies,
there are no known adverse effects of CL0145A to non-target species such as ciliates, other
bivalves, or fish. Case studies at power plants conducted by Molloy indicated that kill rates of
>95% were accomplished at a concentration of 100 ppm of dry bacterial mass per unit volume
for duration of6 hours (Molloy 2002).
Spawning Inhibition
Zebra mussel spawning can be inhibited with various chemicals that target serotonin reuptake.
Selective serotonin reuptake inhibitors can be blocked by receptor antagonists, such as
cyproheptadine and mianserin (Fong et al. 2003). Fong and coworkers (2003) have shown that
low concentrations of these inhibitors can be utilized to block both spawning and parturition in
males and females. Other antagonists such as tricyclic antidepressants have been studied in
relation to zebra mussel spawning. Hardege and coworkers found that imipramine and
desipramine can inhibit male spawning and clomipramine can inhibit both male and female
spawning (Hardege et al. 1997).
V-14
Review of Potential Control Methods