The objectives of the research program reported upon here were (1) to measure ambient levels of UV radiation and determine whichvariables most strongly affected its attenuation in the waters of the estuary and Gulf of St. Lawrence, Canada; and (2) to investigate the potential direct impacts of W radiation on species of crustacean zooplankton and fish whose early life stages are planktonic. In this geographic region, productivity-determining biophysical interactions occur in the upper 0 to 30 m of the water column. Measurements of the diffuse attenuation coefficients for ultraviolet-B radiation ( W -B , 280 to 320 nm) at various locations in this region indicated maximum 10% depths (the depth to which 10% of the surface energy penetrates at a given wavelength) of 3 to 4 m at a wavelength of 310 nm. Organisms residing in this layer-including the eggs and larvae of Calanus finmarchicus and Atlantic cod Gadus morhua-are exposed to biologically damaging levels of W radiation. As a result of these physical and biological characteristics, this system offered a relevant opportunity to assess the impacts of UV on subarctic marine ecosystems. Eggs of C. finmarchicus were incubated under the sun, with and without the W -B and/or UV-A (320 to 400 nm) wavebands. W-exposed eggs exhibited low percent hatchmg compared to those protected from W : W radiation had a strong negative impact on C. finmarchicus eggs. Further, percent hatching in W-B-exposed eggs was not significantly lower than that in eggs exposed to UV-A only: under natural sunlight, UV-A radiation appeared to be more detrimental to C. finmarchicus embryos than was UV-B. In analogous experiments with Atlantic cod eggs, exposure to UV-B produced a significant negative effect. However, UV-A had no negative effect on cod eggs. Additional experiments using a solar simulator (SS) revealed high wavelength-dependent mortality in both C. finmarchicus and cod embryos exposed to UV. The strongest effects occurred under exposures to wavelengths below 312 nm. At the shorter wavelengths (<305 nm) UV-B-induced mortality was strongly dose-dependent, but (for both C. finmarchicus and cod) not significantly influenced by dose-rate. Thus, at least within the limits of the exposures under which the biological weighting functions (BWFs) were generated, reciprocity held. The BWFs derived for UV-B-induced mortality in C. finmarchicus and cod eggs were similar in shape to the action spectrum for UV-B effects on naked DNA. Further, the wavelengthdependence of DNA damage was similar to that for the mortality effect. These observations suggest that W-induced mortality in C. finmarchicus and cod eggs is a direct result of DNA damage. There was no evidence of a detrimental effect of UV-A radiation in these SS-derived results. A mathematical model that includes the BWFs, vertical mixing of eggs, meteorological and hydrographic conditions, and ozone depletion, indicates that W-induced mortality in the C. finmarchicus egg population could be as high as 32.5 %, while the impact on the co...

Abstract:In the Gulf of St. Lawrence, Canada, solar ultraviolet B radiation (UV-B, 280-320 nm) penetrates a significant percentage of the summer mixed-layer water column: organisms residing in this layer, such as the eggs of Atlantic cod (Gadus morhua), are exposed to UV-B. In outdoor exposure experiments, Atlantic cod eggs were incubated in the presence versus the absence of UV-B and (or) UV-A (320-400 nm). We tested two hypotheses: H 1 , UV-B induces mortality in Atlantic cod eggs, and H 2 , UV-A either exacerbates or mitigates any such UV-B-induced mortality. Hypothesis H 1 was supported: there was a significant mortality effect on Atlantic cod eggs exposed to UV-B at the surface and at a depth of 50 cm. Hypothesis H 2 was not supported: there was no effect of UV-A. These experiments indicate that Atlantic cod eggs present in the first metre of the water column (likely only a small percentage of the total egg population) are susceptible to UV-B. However, UV-B must be viewed as only one among many environmental factors that produce the very high levels of mortality typically observed in the planktonic early life stages of marine fishes.Résumé : Dans le golfe du Saint-Laurent (Canada), le rayonnement solaire ultraviolet B (UV-B, 280-320 nm) pénètre une partie importante de la couche de mélange estivale. Les organismes présents dans cette partie, comme les oeufs de morue franche (Gadus morhua), se trouvent exposés aux UV-B. Dans des essais extérieurs d'exposition, des oeufs de morue franche ont été incubés en étant exposés ou non aux UV-B et (ou) aux UV-A (320-400 nm). Nous avons testé deux hypothèses : H 1 , les UV-B entraînent une mortalité chez les oeufs de morue franche, et H 2 , les UV-A accentuent ou atténuent l'éventuel effet létal des UV-B sur les oeufs. L'hypothèse H 1 a été corroborée : on a observé une mortalité significative des oeufs exposés aux UV-B à la surface et à une profondeur de 50 cm. L'hypothèse H 2 a été rejetée : les UV-A n'avaient pas d'effet. Ces expériences montrent que les oeufs de morue franche présents dans le premier mètre de la colonne d'eau (qui ne constituent probablement qu'un faible pourcentage de la population totale d'oeufs) sont sensibles aux UV-B. Cependant, les UV-B ne sont qu'un des nombreux facteurs environnementaux responsables des très forts taux de mortalité habituellement observés chez les premiers stades planctoniques des poissons marins.[Traduit par la Rédaction] Béland et al. 1067

In previous work, we evaluated the effects of ultraviolet (UV 5 280-400 nm) radiation on the early life stages of a planktonic Calanoid copepod (Calanus finmarchicus Gunnerus) and of Atlantic cod (Gadus morhua). Both are key species in North Atlantic food webs. To further describe the potential impacts of UV exposure on the early life stages of these two species, we measured the wavelength-specific DNA damage (cyclobutane pyrimidine dimer [CPD] formation per megabase of DNA) induced under controlled experimental exposure to UV radiation. UV-induced DNA damage in C. finmarchicus and cod eggs was highest in the UV-B exposure treatments. Under the same spectral exposures, CPD loads in C. finmarchicus eggs were higher than those in cod eggs, and for both C. finmarchicus and cod embryos, CPD loads were generally lower in eggs than in larvae. Biological weighting functions (BWF) and exposure response curves that explain most of the variability in CPD production were derived from these data. Comparison of the BWF revealed significant differences in sensitivity to UV-B: C. finmarchicus is more sensitive than cod, and larvae are more sensitive than eggs. This is consistent with the raw CPD values. Shapes of the BWF were similar to each other and to a quantitative action spectrum for damage to T7 bacteriophage DNA that is unshielded by cellular material. The strong similarities in the shapes of the weighting functions are not consistent with photoprotection by UV-absorbing compounds, which would generate features in BWF corresponding to absorption bands. The BWF reported in this study were applied to assess the mortality that would result from accumulation of a given CPD load: for both C. finmarchicus and cod eggs, an increased load of 10 CPD Mb 21 of DNA due to UV exposure would result in approximately 10% mortality.

In previous work, we evaluated the effects of ultraviolet (UV = 280-400 nm) radiation on the early life stages of a planktonic Calanoid copepod (Calanus finmarchicus Gunnerus) and of Atlantic cod (Gadus morhua). Both are key species in North Atlantic food webs. To further describe the potential impacts of UV exposure on the early life stages of these two species, we measured the wavelength-specific DNA damage (cyclobutane pyrimidine dimer [CPD] formation per megabase of DNA) induced under controlled experimental exposure to UV radiation. UV-induced DNA damage in C. finmarchicus and cod eggs was highest in the UV-B exposure treatments. Under the same spectral exposures, CPD loads in C. finmarchicus eggs were higher than those in cod eggs, and for both C. finmarchicus and cod embryos, CPD loads were generally lower in eggs than in larvae. Biological weighting functions (BWF) and exposure response curves that explain most of the variability in CPD production were derived from these data. Comparison of the BWF revealed significant differences in sensitivity to UV-B: C. finmarchicus is more sensitive than cod, and larvae are more sensitive than eggs. This is consistent with the raw CPD values. Shapes of the BWF were similar to each other and to a quantitative action spectrum for damage to T7 bacteriophage DNA that is unshielded by cellular material. The strong similarities in the shapes of the weighting functions are not consistent with photoprotection by UV-absorbing compounds, which would generate features in BWF corresponding to absorption bands. The BWF reported in this study were applied to assess the mortality that would result from accumulation of a given CPD load: for both C. finmarchicus and cod eggs, an increased load of 10 CPD Mb(-1) of DNA due to UV exposure would result in approximately 10% mortality.

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.