Assessing the lethal effects of granular Bayluscide® on the early life stages of the freshwater mussel <i>Lampsilis siliquoidea</i>

Effective control of invasive sea lamprey (Petromyzon marinus) populations relies heavily on lampricides, but few studies have investigated the impacts of granular Bayluscide® (gB) on benthic dwelling organisms. Native freshwater mussels are present in many similar habitats that larval sea lamprey prefer, making them susceptible to non-target effects. The active ingredient of gB, niclosamide, was derived specifically as a molluscicide, therefore it is crucial to understand its impacts on a group of mollusks that have been imperiled due to many factors including the input of contaminants in the aquatic environment. Two early life stages of Lampsilis siliquoidea were tested in 7-day exposures to gB. Mortality was significant in both sub-adult and newly metamorphosed mussels, with the latter being significantly sensitive to gB applications that were less than 1% of the suggested application rate. A significant decrease in mussel growth was seen at 0.78% of the suggested application rate. A 24-hr test was supplemented due to gB potency, revealing a similar median lethal concentration of 0.67% (0.55-0.79) of the suggested gB application rate. Additionally, an 8-hr exposure of 0.78% of the application revealed significant effects after only 2 hr of exposure. Both early life stages of L. siliquoidea showed a marked sensitivity to gB. Although environmental conditions may have an influence on gB fate, the marked sensitivity of early life stages demonstrated in this study is crucial to understanding the effects of sustained gB application on the population dynamics of freshwater mussels.