Modeling the effects of ultraviolet radiation on embryos of Calanus finmarchicus and Atlantic cod (Gadus morhua) in a mixing environment

It is well established that ultraviolet radiation (UVR, 280-400 nm) harms a quatic organisms. Reductions in productivity have been reported for phytopl ankton, ichthyoplankton, and zooplankton in incubations exposed to WR. It i s difficult, however, to estimate the effects of UVR in natural waters. Qua ntitative assessments of UVR effects on aquatic organisms require high-reso lution measurements of solar irradiance and its attenuation in the water, s pectral weighting functions for biological effects, and realistic descripti ons of the distributions and vertical movements of particles in the water c olumn. Using experimentally determined biological weighting functions for U V-induced mortality along with measurement-based models of solar irradiance and of vertical distributions of embryos as influenced by mixing, we model ed UVR-induced mortality in the early life stages of two key species in the upper estuary and Gulf of St. Lawrence, Atlantic cod (Gadus morhua) and th e planktonic copepod, Calanus finmarchicus. G. morhua embryos are insensiti ve to UVR, with an average daily survival of similar to 99% over numerous e nvironmental conditions. C. finmarchicus are considerably more vulnerable, with an average survival of 90% +/- 12% (SD). Lowest modeled daily survival was 59% under ambient ozone and 49% under 50% ozone loss. A sensitivity an alysis allowed us to examine the relative influences of hydrographic variab ility, meteorological conditions, and ozone depletion on UVR-induced mortal ity in C. finmarchicus embryos. The modeled hydrographic and meteorological conditions are a representative range of natural variability for the St. L awrence region during the 1997 held season, with the exception of extreme o zone depletion (50%). Effects are expressed as relative change of survival normalized to survival under a reference simulation. Similar to other studi es, water column mixing and water clarity have the most significant influen ce on embryo survivorship, with a 3%-80% increased chance of survival when in static, compared with mixed waters, and a 3%-46% increased chance of sur vival when in the darkest, compared with the dearest waters. Cloudy skies i ncrease survivorship between 1%-30%, and ozone depletion of 50% can decreas e survivorship by 9%. On average, ozone depletion decreases survival by 3% and of the factors considered has the smallest influence on mortality of C. finmarchicus embryos.