Growing Safe: Acute Size Escape from Desiccation in Juvenile Crepipatella peruviana (Mollusca: Gastropoda)

Desiccation is an important limiting factor in the intertidal zone. Generally decreasing seaward, desiccation stress can also be alleviated in wet microhabitats. Juvenile snails are generally more susceptible to desiccation than adults, and, for some species, juveniles must therefore hide in microhabitats to survive emersion. The transition from hiding in safe microhabitats to being able to survive fully exposed for the duration of low tide is not well documented. In this study, we investigated the influence of size on desiccation tolerance in juveniles of the calyptraeid gastropod Crepipatella peruviana to determine the size at which they can first survive exposure to air. Juveniles 2-13 mm long were exposed to 75% or 100% relative humidity for 0.5-6.5 hours. Juveniles smaller than 5 mm in shell length did not survive emersion at 75% relative humidity for even 0.5 hours; surprisingly, most also perished after short exposures to air at 100% relative humidity, suggesting that something other than desiccation stress may also be at play. In marked contrast, 82% of juveniles larger than 6 mm in shell length survived exposure to 75% relative humidity for the full 6.5 hours. In a field survey, no juveniles smaller than 9 mm were found on exposed rock but rather were found only in wet microhabitats. We suggest that the clearly defined size escape from desiccation may reflect a change in gill functioning or a newfound ability to retain water more effectively within the mantle cavity at low tide.