Blood osmotic concentrations in the three zoeal stages, megalops stage, and adults were determined over a wide range of salinities for the estuarine, grapsid crab, Sesarma reticulatum Say. 2. Larvae are hyper-osmotic over the salinity range 10 to 35‰ and hyper- or isosmotic at 40‰ throughout zoeal and early megalopa life. Older megalops display increased hyper-osmoticity at 10 and 40‰, compared to earlier zoeal stages. 3. Adult specimens of S. reticulatum are hyper-osmotic in the salinity range 5 to 27.5‰, and hypo-osmotic in salinities > 27.5‰. The adult response is apparently attained during early juvenile crab stages. 4. The effects of molting on blood osmotic concentrations is discussed. The rapid molting cycles of the larvae do not affect the blood osmotic concentration. 5. The general larval trend of hyper-osmoticity over wide ranges of external salinities may serve to increase the density of the larva, helping to promote retention within the estuary. Hyper-osmoticity may also act to provide turgor pressure to insure integrity of the thin larval cuticle.
No takes yet. Share an insight, caveat, or question.
J. Kevin Foskett (1977) studied this question.