OSMOREGULATION IN THE LARVAE AND ADULTS OF THE GRAPSID CRABSESARMA RETICULATUMSAY

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Abstract
Osmoregulation in the larval and adult stages of the grapsid crab S. reticulatum was examined. Cryoscopic methods showed that larvae are hyper-osmotic over the entire range of salinities encountered by them in nature. This response changes little throughout zoeal development. Older megalops display slightly greater hyperosmoticity at 10 and 40%. Adults display marked capabilities of osmoregulation; this response is probably attained during the early juvenile crab stages. Molting had no effect on larval body-fluid concentrations. Hyperosmoticity over the entire range of salinities encountered by the larvae in nature may serve as a mechanism to increase the density of the larva, enabling it to remain near the bottom, helping to promote retention within the the estuary. Hyperosmoticity may serve to provide turgor pressure, thereby insuring integrity of the thin larval cuticle.