EFFECT OF FRESHENING ON VARIOUS DEVELOPMENT STAGES OF SEA-URCHINS OF THE GENUS STRONGYLOCENTROTUS

Response to decreased salinity of two species of sea urchins Strongylocentrotus nudus and S.intermedius was investigated at various stages of ontogenesis. The lower limit of salinity tolerance was 22 parts per thousand for S.nudus and 24 parts per thousand for S.intermedius; there was a 100% mortality within 5 days at 24 parts per thousand and 20 parts per thousand respectively. The zone of optimal activity of spermatozoa was limited to 24 parts per thousand for S.nudus and 26 parts per thousand for S.intermedius. Salinity of not less than 26 parts per thousand was required for the normal development of both species at early stages of ontogenesis. All the investigated larvae stages were more tolerant and resistant to the effect of extremely low salinity than adults.