Assessment of Open Water Zequanox Applications for Controlling Dreissenid Mussels within an Inland Lake

Science Center Objects

Invasion of dreissenid mussels (zebra and quagga mussels, Dreissena polymorpha and D. rostriformis bugensis, respectively) into the Great Lakes and Mississippi River Basins has resulted in estimated economic impacts as high as $1 billion annually for maintenance and repair of biofouled water conveyance systems and other infrastructures (Pimentel et al. 2005). 

Environmental and ecosystem level impacts of dreissenids have included shifts in nutrient cycles and food webs, alteration of fish communities, increases in the occurrence and abundance of nuisance algae and aquatic vegetation, as well as associations with harmful algal blooms and Type E botulism outbreaks (Vanderploeg et al. 2001, Higgins and Vander Zanden 2010, Mackie and Claudi 2010, Mayer et al. 2014; Pérez-Fuentetaja et al 2014). One of the most significant ecological impacts of dreissenids has been the sharp decline and extirpation of native unionid mussel populations within infested waters (Schloesser et al. 1996, Ricciardi et al. 1998, Strayer and Malcom 2007, Mackie and Claudi 2010).

Despite efforts of natural resources agencies to prevent their spread, by 1992, dreissenids had  spread to all of the Great Lakes and the Arkansas, Cumberland, Hudson, Illinois, Mississippi, Ohio, and Tennessee Rivers and, by 1994, dreissenids were reported within the borders or in adjacent waterways of 20 states (Benson et al. 2017). Although dreissenids have been pervasive and problematic for decades, control tools with potential for use in open water systems were not available until recently. In the1990’s, researchers at the New York State Museum Field Research Laboratory discovered that a specific strain of the common soil bacterium Pseudomonas fluorescens (Pf-CL145A) caused mortality in dreissenid mussels. Dreissenids readily ingest Pf-CL145A cells as a food source and after ingestion metabolites associated with the bacterium’s cell wall degrades the mussel’s digestive system, resulting in death. Marrone Bio Innovations, Inc. acquired the rights to Pf-CL145A and registered a commercially produced formulation with the trade name Zequanox. Zequanox was first registered by the United States Environmental Protection Agency (EPA) in 2012 for use in defined discharge water conveyance systems (e.g., infrastructures for energy producers and manufacturing companies) and in 2014 the label for Zequanox was expanded to include open water applications for dreissenid mussel control in lakes, rivers, and other waterbodies. Currently, Zequanox is the only EPA registered molluscicide that has demonstrated toxicity to dreissenids and minimal impacts to native Unionid mussels (Luoma et al. 2015a, Luoma et al. 2015b).

Since registration in 2014, only limited-scale Zequanox applications have been conducted in open water systems and applications were contained with barriers (Luoma et al. 2015c, Whitledge et al. 2015). Zequanox applications using barriers limits the depth and treatment area and it also dramatically increases treatment cost and associated labor. Previous studies have demonstrated, with varying degrees of success, that benthic application of Zequanox within quiescent waters has the potential to reduce the amount of Zequanox applied and to eliminate the need for barrier systems (Luoma et al. 2015c, Luoma et al. 2015d, Weber 2015). Additional laboratory and mesocosm-scale application investigations were completed to determine the relationships of water temperature, Zequanox stock concentration, and Zequanox stock viscosity on the stratification of Zequanox during applications in quiescent water (Severson and Luoma 2016). Additional field-scale studies are required to determine the efficacy and feasibility of unbarriered Zequanox applications within open-water systems.

USGS scientists applying Zequanox to evaluate its use as a control for mussels.

USGS scientists applying Zequanox to evaluate its use as a control for mussels.

(Credit: Jim Luoma, Upper Midwest Environmental Science Center. Public domain.)



The study objectives are 1) to determine the efficacy of unbarriered, open-water Zequanox applications for controlling zebra mussel populations by measuring/monitoring Zequanox concentrations and zebra mussel (Dreissena polymorpha) mortality within the treatment plots after Zequanox application, and 2) to determine the potential use of unbarriered Zequanox applications for maintaining Unionid mussel populations within invaded systems by assessing the impact of Zequanox treatments on Unionid mussel survival and condition and the number of adhering zebra mussels. The study involves conducting and evaluating Zequanox applications in a small Midwestern inland lake (Round Lake, Emmet County, MI) in cooperation with the Tip of the Mitt Watershed Council and Marrone Bio Innovations. Results of four replicated 0.30 hectare (Ha; 0.75 acre) Zequanox treated plots will be compared to the results of four replicated 0.30 Ha untreated plots. Zequanox concentration, water chemistry parameters, zebra mussel mortality, zebra mussel density, native mussel condition, and native mussel mortality will be assess/monitored during the exposures and up to 1 year after exposure.