The Effects of Ultraviolet Irradiation on Larvae and Eary Juveniles of the Sea Urchin, Strongylocentrotus intermedius

Abstract

Planktonic larvae and just settled juveniles of the sea urchin, Strongylocentrotus intermedius, were irradiated with various quantities of UV rays, and the effects 24 hrs after keeping them under a condition 10 L:14 D at 16°C (larvae) or 17°C (juveniles) were observed. The results showed that blastula and pluteus larvae were seriously damaged by irradiation of UV-B (280-320nm) and UV-A (320-400nm). A critical dose of damaging UV (DUV) which induced more than 30% morphologi-cally abnormal larvae was 0.01kJ/m² for blastula and 4-armed larvae. It gradually increased to 0.05 and 0.08kJ/m² as the stage advanced to the 6-armed and 8-armed stages, respectively. No effects were observed for juveniles after 24hrs of irradiation of 0.7kJ/m² DUV, but all the juveniles which received more than 0.2kJ/m² died within 1 month. It was suggested that the reproduction of the sea urchin might be affected by sun light in shallow water, since a maximum of the mean daily amount of DUV was reported to be 0.7kJ/m² in July, 1994, in Sapporo.