Influence of UVB radiation on hatching success of marine copepod Paracalanus parvus s. 1

Influence of UVB radiation (UVBR) on hatching success of the marine copepod Paracalanus parvus s. 1. was determined in the laboratory using UVB lamps and the same effect was confirmed in the field under natural solar radiation condition. Hatching success antisigmoidally decreased with UVB dose. The dose-specific mortality of eggs was higher when the UVBR exposure included shorter wavelength than 290 nm. The UVB dose which decreased the hatching success by 50% (LD50) showed that P parvus egg was more sensitive to UVB than other previously reported marine copepods. UVB-induced influence was not a simple function of UVB dose but also of UVB exposure time. Relatively long exposure of low UVBR was more detrimental than a short exposure of high UVBR for equal cumulative doses. Sensitivity to UVB decreased with time after spawning. After exposure to solar UVBR, the hatching success decreased in a similar manner to the experiment using UVB lamps. The depths where 10% and 20% egg mortalities are expected were estimated as 1.4 and 3.0 m, respectively, assuming the median attenuation coefficient of UVBR at 305 nm in the water off Hokkaido (0.44 m-1) and the same solar UVBR during the experiment. Solar UVBR at mid-latitude area is estimated as a factor affecting the recruitment of P. parvus even under the present level of ozone concentration.