The effects of changes in temperature and salinity on the quality of shells selected by the hermit crab Pagurus longicarpus

Intertidal zones are highly dynamic environments. At low tide, temperatures and salinities in intertidal tide pools can change substantially and quickly, depending on the weather conditions on a given day and the volume of water in the pools. As we begin to feel the effects of climate change more strongly, conditions in tide pools will likely become even more extreme. The long-wristed hermit crab Pagurus longicarpus can be found intertidally and subtidally along the Atlantic coast of North America from Nova Scotia to Florida, as well as along the Gulf coast. At low tide, they can often be found in tide pools. We tested the effects of temperature, salinity and their combination on the ability of hermit crabs to select high-quality shells of appropriate size over relatively small shells and shells that had been drilled by predatory snails. Exposing hermit crabs to a temperature of 33°C and a salinity of 40 ppt after a gradual increase from 21°C and 30 ppt had the greatest effect on the quality of shells occupied by the hermit crabs over the next 24 h, compared with shells occupied by hermit crabs that remained at the control temperature and salinity of 21°C and 30 ppt. Changing the temperature and salinity to 30°C and 40 ppt also had a noticeable effect on shell choice, as did increasing the temperature alone to 33°C. Our results suggest that as the planet warms and precipitation patterns change, intertidal hermit crabs of the species P. longicarpus will likely more often be found occupying shells that are damaged or not of an appropriate size, leaving the hermit crabs more exposed to predation, desiccation and other stressors.