EFFECTS OF CHEMICAL CUES ON SETTLEMENT BEHAVIOR OF BLUE-CRAB CALLINECTES-SAPIDUS POSTLARVAE

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