EFFECTS OF ADULT SALINITY ACCLIMATION ON LARVAL SURVIVAL AND EARLY DEVELOPMENT OF STRONGYLOCENTROTUS-DROEBACHIENSIS AND STRONGYLOCENTROTUS-PALLIDUS (ECHINODERMATA, ECHINOIDEA)

Larval survival and development rates of Strongylocentrotus droebachie nsis and Strongylocentrotus pallidus were determined as a function of salinity in two experiments by (i) directly transferring fertilized eg gs obtained from adults acclimated to seawater at a salinity of 30 par ts per thousand, to cultures containing seawater at salinities of 30, 27.5, 25, 22.5, 20, 17.5, 15, 12.5, and 10 parts per thousand, at 10 d egrees C; and (ii) acclimation of adult sea urchins to the salinity -t emperature conditions described above for 2, 3, and 4 weeks prior to s pawning. Subsequent development occurred under these acclimation condi tions. Development rates and percent survival of larvae prior to metam orphosis varied directly with salinity. Survival of S. pallidus plutei to metamorphosis decreased at salinities below 30 parts per thousand. Stronglyocentrotus droebachiensis plutei survived to metamorphosis at 20 parts per thousand, and above. Lactic acid concentrations in the c oelomic cavity fluid of adult S. droebachiensis and S. pallidus acclim ated to low salinity were significantly higher than initial controls a t 30 parts per thousand. Cell volumes of fertilized eggs of both speci es exhibited osmotic swelling when exposed to lowered salinity. LC(50) values (parts per thousand), development rates, and percent survival to metamorphosis indicate that acclimation of adult urchins to lower s alinity prior to spawning and fertilization does not enhance developme nt or survival of embryos of these two species exposed to low salinity . Furthermore, our results show that S. pallidus larvae are stenohalin e when compared with larvae of other echinoderm species.