Ontogeny of salinity tolerance and hyper-osmoregulation by embryos of the intertidal crabs Hemigrapsus edwardsii and Hemigrapsus crenulatus (Decapoda, Grapsidae): Survival of acute hyposaline exposure

Abstract The adults of Hemigrapsus edwardsii and Hemigrapsus crenulatus are euryhaline crabs and strong hyper-osmoregulators. Their embryos are carried externally attached to the abdominal pleopods of female crabs, where they are exposed to temporal and spatial changes in salinity associated with their intertidal and estuarine habitats. Although embryos lack the branchial and excretory organs responsible for adult osmoregulation, post-gastrula embryos were highly tolerant of exposure to hypo-osmotic sea water. Detached eggs (embryos + envelopes), of both species, at all developmental stages between gastrulation and hatching, exhibited 80–100% survival for periods up to 96 h in sea water (osmolality, 1050 mmol kg − 1 ) and in dilutions to 50%, 10%, and 1%. Cleavage stages were less tolerant of dilution; H. edwardsii , H. crenulatus − 1 above external). Osmoregulatory capacity was reduced just prior hatching, particularly in H. crenulatus , although salinity tolerance remained high. Gastrulation therefore marks a critical stage in the ontogeny of osmoregulation and salinity tolerance. Total Na + /K + -ATPase activity increased greatly during embryogenesis of H. crenulatus (undetectable in blastulae; gastrulae 0.31 ± 0.05 pmol P i embryo − 1 min − 1 ; pre-hatching 16.4 ± 1.0 pmol P i embryo − 1 min − 1 ). Na + /K + -ATPase activity increased in embryos exposed to dilute sea water for 24 h implicating regulation of this transporter in a short-term acclimation response.