Effects of chemical and physical conditions on hatching success of Bythotrephes longimanus resting eggs

Dormant eggs of zooplankton are considered to be tolerant of harsh environmental conditions, yet lethal thresholds of exposure have rarely been determined. We describe 3 yr of dose-response experiments that evaluate hatching success of the resting egg of Bythotrephes longimanus (Cladocera: Cercopagidae) in response to salinity, chlorination, heat, desiccation, and freezing. There was no decline in hatching success in response to salinity (up to 4 weeks at 35 g L-1 salt) or chlorination (including up to 5 min at 3400 mg L-1 chlorine). In response to heat there was an interaction between time and temperature; hatching occurred after exposure to 40 degrees C for 1 min, 5 min, or 10 min but declined with the two longer exposures. Hatching also occurred after exposure to 50 degrees C for 1 min, but no hatching followed exposure to 50 degrees C for 5 min or to higher temperatures for 1 min. In response to desiccation at 17 degrees C, exposure for <= 4 h had no effect on hatching but >= 6 h resulted in no hatching. When frozen, hatching success depended on whether eggs were frozen in water or without water. Collectively, the results are congruent with an evolutionary origin of B. longimanus in permanent, euryhaline basins. The results advance our understanding of dispersal limits of B. longimanus, including vector potential, and may inform management practices for reducing range expansion of B. longimanus by humans.