Effects of environmental cues on metamorphosis of the blue crab Callinectes sapidus

of the blue crab Caflinectes sapldus (Rathbun) are transported from shelf/coastal areas into estuanes where they metamorphose (molt) to the fiht crab stage. This study used time to metamorphosls o f megalopae collected near the entrance to estuaries as a measure of the effectiveness of cues in estuanes 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 die1 rhythm, in which megalopae preferentially molted during the day. Metamorphosis was delayed in offshore water and accelerated in estuarine water The active chemlcal cues in esluaries were primarily < l 0 kDa, and they varied in potency between estuaries. Megalopae d ~d 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 altern~nora xcelerated 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 speaes. These results support the hypothesis of Wolcott & DeVnes (1994; Mar Ecol Prog Ser 109:15?-163L 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 a f metamorphosls by cues from a variety of plants 1s useful IF megalopae are transported to different estwhes and areas within estuar~es that have different aquatic vegetation.