Impact of solar ultraviolet radiation on hatching of a marine copepod, Calanus finmarchicus

The calanold copepod Calanus finmarchicus 1s a key component of the zooplankton community in the estuary and Gulf of St. Lawrence, Canada. During the spring and summer months, C. firmarchicus eggs are released into the shallow (0 to 15 m) mixed surface layer, where they incubate for 1 to 3 d. Radiometric measurements in this region show that biologically significant levels of solar ultraviolet radiation (UV = 280 to 400 nm) penetrate into the mixed surface layer. Thus, C. finmarchicus eggs are potentially susceptible to UV-induced mortality. This possibility was evaluated by incubating C. finmarchicus eggs in an outdoor reservoir under natural sunlight. There were 3 spectral exposures regimes [UV-B (280-320 nm) + UV-A (320-400 nm) + PAR (400-700 nm); UV-A+PAR; PAR only]. Control groups were kept in the dark. Incubations were conducted at depths of 2 and 60 cm and the percentage of eggs that hatched was determined following 2 to 3 d exposures in 3 independent experiments. Both the UV-BtUV-A+PAR and the UV-A+PAR treatments exhibited low percent hatching compared to the PAR and dark treatments: UV radiation had a strong negative impact on C. finmarchicus eggs. Further, percent hatching in UV-B-exposed eggs was not significantly lower than that in eggs exposed to UV-A only: under natural sunlight, W-A radiation appeared to be more detrimental to C. finmarchcus embryos than W-B. UV penetration into the experimental reservoir was similar to that observed in estuarine waters of this region, but lower than the clearer waters of the Gulf of St. Lawrence. This suggests that, at current levels of exposure, UV radiation has a negative effect on C. finmarchicus eggs residing in the first few meters of the water columns in this geographic region