MEPS 131:165-177 (1996)  -  doi:10.3354/meps131165

Postlarvae (megalopae) of the blue crab Callinectes sapidus (Rathbun) are transported from shelf/coastal areas into estuaries where they metamorphose (molt) to the first crab stage. This study used time to metamorphosis of megalopae collected near the entrance to estuaries as a measure of the effectiveness of cues in estuaries to induce metamorphosis. Daily feeding and water change had no effect on the time to metamorphosis, but the time increased as the density of larvae increased. There was a diel rhythm, in which megalopae preferentially molted during the day. Metamorphosis was delayed in offshore water and accelerated in estuarine water. The active chemical cues in estuaries were primarily <10 kDa, and they varied in potency between estuaries. Megalopae did not preferentially metamorphose in the estuary where they were collected, which suggests that the concept of preferential recruitment to a home estuary is incorrect. Exposure to 3 species of seagrasses and the salt marsh cord grass Spartina alterniflora accelerated metamorphosis. In each case, chemical cues from the plants mimicked the response to the plants, but structural cues alone had no effect. Responses to macroalgae varied greatly with species. These results support the hypothesis of Wolcott & DeVries (1994; Mar Ecol Prog Ser 109:157-163) that metamorphosis is delayed in offshore water and accelerated by cues associated 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.

Blue crab . Callinectes sapidus . Megalopae . Metamorphosis . Chemical cues