OFFSHORE MEGALOPAE OF CALLINECTES-SAPIDUS - DEPTH OF COLLECTION, MOLT STAGE AND RESPONSE TO ESTUARINE CUES

Megalopae of Callinectes sapidus from offshore waters can shorten the interval to metamorphosis to first crab in response to cues common to settlement habitat within estuaries. Observations were made on postlarvae (megalopae) collected offshore from the Chesapeake Bay (USA) over a period of several days in October 1992, fairly late in the recruitment season. Megalopae exposed to a combination of water from the marsh surface and low salinity accelerated metamorphosis by 10%. Physiological condition of postlarvae collected both in surface waters and from the bottom was compared, using molt stage, progress to molt, and survivorship as indicators. No differences in physical condition were detected, and no megalopae were in active premolt. The pattern of progress to metamorphosis implies that both benthic and surface postlarvae are able to delay metamorphosis, and that the initiation of behaviors that move megalopae from surface waters is temporally segregated from advance to metamorphosis.