Vitality of plaice embryos (Pleuronectes platessa) at moderate UV-B exposure

The effects of moderate UV-B radiation (280-320 nm) on mortality and on phy siologically vital parameters (heart rate, quality of respiratory control) were studied in plaice embryos (Pleuronectes platessa L.). If UV-B exposure started at the early embryonic stage Ib (with a daily dose similar to pres ent maximum outdoor levels in mid-April: 4.86 kJ m(-2)), 100% of embryos we re dead after 5 days (control: 61% mortality). If light exposure started la ter (after gastrulation at stage II), however, mortality in test (UV-B irra diated) and control embryos (not W-B irradiated) was not significantly diff erent. Instantaneous or short-term effects of UV-B exposure on heart rate w ere absent even at high intensity (0.5 W m(-2)). With exposure to a daily d ose of 4.86 kJ m(-2), long-term accumulated effects of W-B on heart rate we re not detectable: heart rate in test and control embryos increased similar ly during development from stage III gamma to hatching. Exposure for a few days at a daily dose of 8.64 kJ m(-2) (similar to present maximum outdoor l evels in mid-May), however, resulted in significantly lower heart rates in test embryos than in control embryos at stage IV beta. Even 45 days after e xposure, sublethal effects of W-B on dry weight of the larvae, heart rate a nd quality of respiratory control were detectable in test animals. It is co ncluded that the vitality of plaice embryos can be impaired, either by rela tively low UV-B doses during early development or by higher UV-B doses duri ng late development. (C) 1999 Elsevier Science B.V. All rights reserved.