AERIAL EXPOSURE TOLERANCE OF ZEBRA AND QUAGGA MUSSELS (BIVALVIA, DREISSENIDAE) - IMPLICATIONS FOR OVERLAND DISPERSAL

We examined the effects of ambient temperature (10, 20, and 30 degrees C) and relative humidity (10, 50, and 95% RH) on the aerial exposure tolerance of adult zebra mussel (Dreissena polymorpha) and quagga muss el (D. bugensis) collected from the St. Lawrence River. Survivorship o f mussels in air significantly increased with increasing RH, decreasin g temperature, and increasing mussel size. At 20 degrees C and 50% RH (early temperate summer conditions), large (21-28 mm) D. polymorpha su rvived more than 5 days exposure, whereas small (10-18 mm) D. polymorp ha survived 1-3 days. Seventy-three percent of large D. polymorpha and 10% of small D. polymorpha survived 10 days exposure at conditions co nsidered optimal for survivorship (10 degrees C and 95% RH). Survivors hip of D. bugensis was tested at 20 degrees C and was 15-100% lower th an that of D. polymorpha at all RH levels combined with exposures less than 5 days. Dreissena bugensis also suffered significantly higher pe rcent weight losses because of desiccation than D. polymorpha. The dif ferences in the desiccation tolerance of zebra and quagga mussels refl ect their relative depth distribution in lakes. Our results suggest th at, given temperate summer conditions, adult Dreissena may survive ove rland transport (e.g., on small trailered boats) to any location withi n 3-5 days' drive of infested waterbodies.