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 physiologically 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 present maximum outdoor levels in mid-April: 4.86 kJ m−2), 100% of embryos were dead after 5 days (control: 61% mortality). If light exposure started later (after gastrulation at stage II), however, mortality in test (UV-B irradiated) and control embryos (not UV-B irradiated) was not significantly different. Instantaneous or short-term effects of UV-B exposure on heart rate were absent even at high intensity (0.5 W m−2). With exposure to a daily dose of 4.86 kJ m−2, long-term accumulated effects of UV-B on heart rate were not detectable: heart rate in test and control embryos increased similarly during development from stage IIIγ to hatching. Exposure for a few days at a daily dose of 8.64 kJ m−2 (similar to present maximum outdoor levels in mid-May), however, resulted in significantly lower heart rates in test embryos than in control embryos at stage IVβ. Even 45 days after exposure, sublethal effects of UV-B on dry weight of the larvae, heart rate and quality of respiratory control were detectable in test animals. It is concluded that the vitality of plaice embryos can be impaired, either by relatively low UV-B doses during early development or by higher UV-B doses during late development.