Effects of chemical cues on settlement behavior of blue crab Callinectes sapidus postlarvae

Settlement of blue crab Callinectes sapidus Rathbun postlarvae (megalopae) was examined in the field in the presence and absence of chemical cues from settlement habitats and potential megalopal predators. Megalopae in premolt preferentially settled on collectors containing seagrasses Zostera marina and Halodule wrightii, but not on collectors with salt marsh cordgrass Spartina alterniflora. Settlement of megalopae was reduced by up to 40% in the presence of predators from several different habitats, including crabs Uca pugilator, U. pugnax and Panopeus herbstii, and grass shrimp Palaemonetes pugio. Laboratory predation assays showed that each of these potential predators ate C. sapidus megalopae if they encountered them. Megalopae avoided odors of U, pugilator in chemotaxis assays, and showed no reaction to odors from Z, marina and S, alterniflora. Settlement of megalopae was unaffected by the presence of adult C. sapidus or brown shrimp Penaeus aztecus, neither of which consumed megalopae in laboratory predation assays. Megalopae showed no reaction to fouled shells of oyster Crassostrea virginica, but avoided live C, virginica. Thus, settling blue crab megalopae can distinguish among settlement sites using chemical cues, and their discrimination ability increases in the premolt stage.