EFFECTS OF ENVIRONMENTAL CUES ON METAMORPHOSIS OF THE BLUE-CRAB CALLINECTES-SAPIDUS

Postlarvae (megalopae) of the blue crab Callinectes sapidus (Rathbun) are transported from shelf/coastal areas into estuaries where they met amorphose (molt) to the first crab stage. This study used time to meta morphosis of megalopae collected near the entrance to estuaries as a m easure of the effectiveness of cues in estuaries to induce metamorphos is. Daily feeding and water change had no ef feet on the time to metam orphosis, but the time increased as the density of larvae increased. T here was a diel rhythm, in which megalopae preferentially molted durin g the day. Metamorphosis was delayed in offshore water and accelerated in estuarine water. The active chemical cues in estuaries were primar ily <10 kDa, and they varied in potency between estuaries. Megalopae d id not preferentially metamorphose in the estuary where they were coll ected, which suggests that the concept of preferential recruitment to a home estuary is incorrect. Exposure to 3 species of seagrasses and t he salt marsh cord grass Spartina alterniflora accelerated metamorphos is. In each case, chemical cues from the plants mimicked the response to the plants, but structural cues alone had no effect. Responses to m acroalgae varied greatly with species. These results support the hypot hesis of Wolcott & DeVries (1994; Mar Ecol Frog Ser 109:157-163) that metamorphosis is delayed in offshore water and accelerated by cues ass ociated with estuaries. The results suggest that the primary cues may be derived from estuarine vegetation. Acceleration of metamorphosis by cues from a variety of plants is useful if megalopae are transported to different estuaries and areas within estuaries that have different aquatic vegetation.