Many aquatic snails occupy ephemeral habitats that are occasionally subjected to severe
environmental conditions. To investigate the physiological capacity of these animals to
resist extreme environmental changes, we aerially exposed pond snails (Physella integra)
to temperatures of 5�C and 20�C for 6, 8, 12, 24, 36, 48, and 60 hours. Survivorship varied
with temperature and exposure times. At 20�C, survivorship was 0% for snails aerially
exposed for 24 hours or longer. At 5�C, 0% survivorship was attained at 60 hours
exposure. Sensitivity to aerial exposure was related to shell size of individuals, with larger
specimens (shell length greater than 7 mm) significantly more likely to survive exposure
than smaller specimens at temperatures and intervals with incomplete mortality. These
results suggest that epiphragm development and size-specific survivorship predispose these
animals to rapid population recovery following severe, short-term environmental
fluctuations.
