Efficacy of recreational watercraft decontamination practices to prevent the spread of aquatic invasive species.
The spread of aquatic invasive species (AIS) is a threat to the biodiversity and ecosystem services of invaded environments, and human activities largely facilitate their dissemination. Recreational boating activities enable the overland dispersal of AIS among disconnected lakes, as invertebrate and plant species can become attached to, caught on, or contained within watercraft and equipment used in invaded waterbodies. As AIS can survive transport aboard fouled watercraft, the Ontario Ministry of Natural Resources and Forestry recommends decontaminating watercraft and equipment by washing them at high pressure, rinsing with hot water, or air-drying all parts for up to seven days to inhibit this mode of secondary spread. There is a lack of studies on the efficacy of several recommended methods, especially under realistic conditions, and that consider their feasibility to implement by recreational boaters. Hence, I conducted experiments addressing this knowledge gap, using AIS present in Ontario, namely zebra mussels, banded mystery snails, spiny waterfleas, Eurasian watermilfoil, Carolina fanwort, and European frogbit. I found that washing at high pressures of 900-1200 psi removed the most biological material (90%) from surfaces. Brief exposure to water at ≥ 60°C caused almost 100% mortality among all species tested, except snails which required water at ≥ 65°C. Additionally, acclimating specimens to a range of temperatures (15°C to 30°C) before hot water exposure had little effect on the minimum temperature required for no survival. Air-drying durations producing complete mortality were ≥ 60h for zebra mussels and spiny waterfleas, and ≥ 6 days among plants, whereas survival remained high among snails after a week of air-drying. Nonetheless, hot water exposure followed by air-drying was more effective than either method separately against all species tested, reducing either the minimum water temperature or air-drying duration necessary. These findings can inform management strategies against the spread of AIS. Although individual methods can be effective, and combining methods improves efficacy while also reducing time or temperatures needed, the best approach would be to sequentially implement several simple measures that target a diversity of species.