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

The calanoid copepod Calanus finmarchicus is a key component of the zooplan kton community in the estuary and Gulf of St. Lawrence, Canada. During the spring and summer months, C. finmarchicus eggs are released into the shallo w (0 to 15 m) mixed surface layer, where they incubate for 1 to 3 d. Radiom etric measurements in this region show that biologically significant levels of solar ultraviolet radiation (UV = 280 to 400 nm) penetrate into the mix ed surface layer. Thus, C, finmarchicus eggs are potentially susceptible to UV-induced mortality. This possibility was evaluated by incubating C, finm archicus 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 (40 0-700 nm); UV-A+PAR; PAR only]. Control groups were kept in the dark. Incub ations were conducted at depths of 2 and 60 cm and the percentage of eggs t hat hatched was determined following 2 to 3 d exposures in 3 independent ex periments. Both the UV-B+UV-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 hatchin g in W-B-exposed eggs was not significantly lower than that in eggs exposed to W-A only: under natural sunlight, UV-A radiation appeared to be more de trimental to C, finmarchicus embryos than UV-B. UV penetration into the exp erimental reservoir was similar to that observed in estuarine waters of thi s region, but lower than the clearer waters of the Gulf of St. Lawrence. Th is suggests that, at current levels of exposure, UV radiation has a negativ e effect on C, finmarchicus eggs residing in the first few meters of the wa ter columns in this geographic region.