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 premoIt preferentially settled on collectors containing seagrasses Zostera n~arina and Halodule wrightii, but not on collectors with salt marsh cordgrass Spartina alternlflora. Settlement of megalopae was reduced by up to 40%) in the presence of predators from several different habitats, ~ncluding crabs Uca puqllator, U. pugnax and Panopeus herbstil, and grass shrimp Palaemonetespuglo. Laboratory predation assays showed that each of these potential predators ate C. sapidus n~egalopae 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 shnmp Penaeus aztecus, neither of which consumed megalopae in laboratory predation assays. hlegalopae showed no reaction to fouled shells of oyster Crassostrea vlrglnica, but a v o ~d e d live C virglnlca. Thus, settling blue crab megalopae can disttnguish among settlen~ent sites using chemlcal cues, and their discrimination ability increases in the premolt stage.