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    Aquatic community response to Zequanox®: a mesocosm experiment

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    Nicholson, Michele
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    Abstract
    Zebra and quagga mussels (Dreissena spp.) are European freshwater molluscs that have invaded

    most major inland water systems across North America, resulting in billions of dollars in damages and

    losses to fisheries, recreational water use, infrastructure, and industry each year. Zequanox®, a

    biopesticide made from soil bacteria, has been advertised as dreissenid-selective and environmentally

    safe. Health Canada has approved the use of Zequanox® in hydroelectric facilities, which may indicate

    movement toward open-water use in Canada, as has occurred in the USA and Ireland. Data from singlespecies

    assays indicate that exposure to Zequanox® concentrations near or below those recommended for

    open-water applications can cause mortality (often ≥50%) in fish and invertebrates. However, little is

    known about the non-target impacts of applying Zequanox® in an open-water setting, given that toxicants

    can behave differently in natural versus laboratory environments and because single-species tests are

    unable to characterize indirect effects such as pesticide-mediated changes to inter-species interactions like

    competition and predation.

    Using a six-week-long replicated aquatic mesocosm experiment, I simulated open-water

    applications of Zequanox® (100 mg/L of the active ingredient) to determine the responses of primary

    producers, zooplankton, and macroinvertebrates to Zequanox® exposure in a complex aquatic

    environment. Short-term increases occurred in phytoplankton and periphyton biomass (250–350% of

    controls), abundance of large cladoceran grazers (700% of controls), and insect emergence (490% of

    controls). Large declines initially occurred among small cladoceran zooplankton (88–94% reductions in

    Chydorus sphaericus, Ceriodaphnia lacustris, and Scapheloberis mucronata), but abundances generally

    rebounded within three weeks. Declines also occurred in amphipods Hyalella azteca (mean abundance

    77% less than controls) and gastropods Viviparus georgianus (survival 73 ±16%), which did not recover

    during the experiment. Short-term impacts to water quality included a decrease in dissolved oxygen

    (minimum 1.2 mg/L), despite aeration of the mesocosms.

    This research may assist regulators and managers in assessing the ecological risks of using

    Zequanox® in open-water systems and support informed decision-making about dreissenid control,

    including for established infestations, rapid response to new invasions, and efforts under the Species at

    Risk Act to protect and restore native mussel habitats that have been threatened and damaged by

    dreissenid invasion.
    URI for this record
    http://hdl.handle.net/1974/23928
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