| dc.description.abstract | 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. | en |
