Differences in body size and water balance strategies between North Carolina and Florida populations of the sand fiddler crab, Uca pugilator

Sand fiddler crabs, Uca pugilator, from North Carolina (NC) are two-times smaller than ones from Florida (FL). A water balance study was conducted to examine this size difference in relation to possible changes in habitat suitability. Like most crabs, U. pugilator are classified as hydrophilic, which is consistent with their preference for humid environments. In contrast to the North Carolina population, U. pugilator-FL loses water less rapidly and has higher percentage body water content, a water balance strategy that emphasizes retention. Conversely, the amount of body water required is less for U. pugilator-NC, enabling it to maintain water balance despite having a higher water loss rate. Both tolerated only about 1/4 loss of body water before succumbing to desiccation. Neither experienced a critical transition temperature, CTT. We concluded that water balance profiles of these two populations are complementary, representing trade-offs that permit survival in a moisture-rich habitat. Lower body water content, however, overlaps with features of arthropods that thrive at low temperature, suggesting that U. pugilator-NC may be more cold tolerant.