Effects of Low pH and High Temperature on Hatching and Survival of the Water Mite Unionicola foili (Acari: Unionicolidae)

Adult females, larvae, and eggs of the water mite Unionicola foili were removed from their host mussel Utterbackia imbecillis, and their tolerance to varying pH (4.1, 5.2, 7.0, and 7.8) and temperature (25°, 33°, and 38° C) was examined. Longevity of adult U. foili was significantly reduced at pH 4.1, whereas survival of larvae was significantly reduced at pH 5.2. Hatching of mite eggs was unaffected by exposure to low pH. Survival of adult mites was significantly reduced when exposed to increasing temperature treatments. Larval mites experienced a significant decrease in survivorship at 33° C, but exposure to higher temperature yielded no further changes in longevity. Egg hatching was not affected by exposure to increasing temperature. Although eggs of U. foili were comparatively more resis- tant to low pH and elevated temperature than adults or larvae, the reason for the observed differences remains to be tested. Overall, U. foili were fairly sensitive to low pH and elevated temperature. Active stages of U. foili appear to be more vulnerable to pH changes than their adult host mussels, making them useful biomonitors of acute exposures to acid-contaminated waters.