Occurrence and Survival of Zebra Mussel (Dreissena polymorpha) Veliger Larvae in Residual Water Transported by Recreational Watercraft

Abstract

Zebra mussels (Dreissena polymorpha) are an aquatic invasive species (AIS) that have spread to many waterbodies in North America and transient recreational watercraft are one of the primary pathways of spread. Best management practices for reducing the risk of spreading AIS include draining all water from watercraft before leaving a water body, but removing all water is impractical. Uncertainly exists about whether zebra mussel larvae (veligers) could reside within the “residual water” that remains after draining and survive overland transport to a new water body. At two Minnesota, USA water bodies (Gull Lake and Lake Minnetonka) from July – August (2016-2017) we collected over 300 samples of residual water from recreational watercraft; compartments included ballast tanks, live wells, sterndrive engines, and others. Roughly half (48%) of these samples contained no veligers and the majority (75%) contained five or fewer. Sterndrive engines and ballast tanks ranked 1st and 2nd for volumes of residual water (median of 4945 and 2650 milliliters, respectively), Ballast tank samples contained the largest median number of veligers per sample (247) and sterndrive engines the highest maximum number of veligers (about 4500 for 2 out of 38 engines sampled). We conducted laboratory experiments on veliger survival in residual water of live wells due to the high frequency of fishing boats moving between water bodies, and ballast tanks given their high likelihood of containing veligers. We exposed live well samples to 20°, 27°, 32°, and 38°C air temperature and ballast tanks to 20° and 32°C. For veligers in live well residual water, we observed greater than or equal to 95% mortality after 5 hours of exposure at all temperatures. These same levels of mortality were reached more slowly in ballast tanks (greater than or equal to 95% mortality at both temperatures achieved at 48 hours). Additional prevention steps should be taken (e.g. using hot water) to reduce the risk of transporting living veligers in residual water.