BRODIE, R.J.; STATON, J.S.; University of South Carolina; University of South Carolina: Freshwater invasion and larval settlement: reinvasion of low salinity adult habitats after marine planktonic development in the fiddler crabs Uca pugilator, Uca pugnax and Uca minax

Many invertebrates that have invaded low salinity and freshwater environments from the sea have retained marine planktonic larval development. In these taxa, early life stages must survive a broad range of physical conditions as they travel from the ocean to settlement sites in areas where adults reside. We investigated the settlement strategies of three brackish water fiddler crabs from the southeastern United States that undergo larval development in coastal marine waters, but live as adults along the banks of tidally-influenced rivers and creeks. Two of these species� U. pugilator and U. pugnax� occupy habitats with intermediate salinities, while U. minax dominates in low salinity and freshwater areas. We collected recently settled crabs along a salinity gradient to address three alternative hypotheses for each species: 1. Young crabs leave the ocean and settle directly into adult habitats. 2. Young crabs invade brackish water environments gradually as they develop and grow, arriving at adult habitats as older juveniles. 3. Young crabs settle randomly throughout brackish water systems, dying out in areas that are not suitable for them. Young individuals from these three fiddler species were identified using a species-specific restriction fragment length polymorphism because they are not distinguishable based on morphology. This work forms the basis for future investigations of the behavioral and physiological adaptations in the early life stages of freshwater invading crabs.