OSTERBERG, J.S.; RITTSCHOF, D.; FORWARD, JR. , R.B.; Duke University Marine Lab: Ontogenic Changes in Chemically Mediated Rheotaxis by Blue Crabs, Callinectes sapidus: Implications for Secondary Dispersal

Secondary dispersal of blue crab (Callinectes sapidus) juveniles from initial settlement habitats (often seagrass beds) to the wider estuarine environment is a crucial step in the blue crab life cycle. If juvenile stage crabs are similar to adults and megalopae then secondary dispersal is a complex issue likely regulated by at least three sets of cues: turbulence, light, and chemical. It has been proposed that secondary dispersal occurs as soon as the first juvenile stage and is density dependent. We, therefore, hypothesize that there are ontogenic switches in behavioral responses to the odors of conspecifics of different juvenile stages or other members of the seagrass community. Here we investigated only the chemical cues we hypothesize to be associated with secondary dispersal. Blue crab megalopae were collected with plankton nets from the Newport River, NC estuary during nighttime flood tides, reared in the laboratory to various juvenile crab stages, and tested for positive and negative rheotactic responses to a range of odor solutions. Crabs were tested in a glass tube with odor solution flow regulated by a flow meter. Positive or negative rheotaxis was scored as movement 5 cm either upstream or downstream, respectively, from the central entry location. Odor solutions tested include offshore seawater control, and odors of blue crab megalopae, juveniles and adults, seagrass, and predators. Some of our results support our hypothesis.