Ability of Some Gastropod Egg Capsules to Protect against Low-salinity Stress

The ability of the egg capsules of three intertidal gastropod species to protect embryos against low-salinity stress was examined. Encapsulated embryos of Ilyanassa obsoleta (Say), Nucella lamellosa (Gmelin), and N. lima (Gmelin) were far more tolerant of transfer to water of reduced salinity than were embryos which had been prematurely removed from egg capsules and transferred to low-salinity sea water directly. However, the walls of N. lamellosa and N. lima capsules were found to be permeable to salts and at least to small carbohydrate molecules (glucose). Correspondingly, indirect evidence for all three species and direct evidence for N. lamellosa indicates that the osmotic concentration of intracapsular fluid declines to near ambient after transfer of egg capsules to dilute medium. Experiments conducted using embryos of N. lamellosa suggest that the egg capsules may protect embryos by reducing the rate at which the osmotic concentration of intracapsular fluid decreases rather than by reducing the magnitude of the decrease.