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

Abstract

It is well established that ultraviolet radiation (UVR, 280-400 nm) harms aquatic organisms. Reductions in productivity have been reported for phytoplankton, ichthyoplankton, and zooplankton in incubations exposed to UVR. It is difficult, however, to estimate the effects of UVR in natural waters. Quantitative assessments of UVR effects on aquatic organisms require high-resolution measurements of solar irradiance and its attenuation in the water, spectral weighting functions for biological effects, and realistic descriptions of the distributions and vertical movements of particles in the water column. Using experimentally determined biological weighting functions for UV-induced mortality along with measurement-based models of solar irradiance and of vertical distributions of embryos as influenced by mixing, we modeled 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 the planktonic copepod, Calanus finmarchicus. G. morhua embryos are insensitive to UVR, with an average daily survival of ϳ99% over numerous environmental conditions. C. finmarchicus are considerably more vulnerable, with an average survival of 90% Ϯ 12% (SD). Lowest modeled daily survival was 59% under ambient ozone and 49% under 50% ozone loss. A sensitivity analysis allowed us to examine the relative influences of hydrographic variability, meteorological conditions, and ozone depletion on UVR-induced mortality in C. finmarchicus embryos. The modeled hydrographic and meteorological conditions are a representative range of natural variability for the St. Lawrence region during the 1997 field season, with the exception of extreme ozone depletion (50%). Effects are expressed as relative change of survival normalized to survival under a reference simulation. Similar to other studies, water column mixing and water clarity have the most significant influence 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 survival when in the darkest, compared with the clearest waters. Cloudy skies increase survivorship between 1%-30%, and ozone depletion of 50% can decrease 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.Long-term data on solar ultraviolet-B radiation (UVB, 280-320 nm) incident at the Earth's surface, although rare,

Dose and dose-rate dependency in the mortality response of Calanus finmarchicus embryos exposed to ultraviolet radiation

“…A biological weighting function (BWF), characterizing wavelength-specific UV-B-induced mortality in C. finmarchicus eggs, was derived from these data (Kouwenberg et al 1999a). This BWF has been used to evaluate the susceptibility of C. finmarchicus populations to UV-B exposure under a variety of scenarios, including those predicted for various percent thinnings of the ozone layer (Kuhn et al 2000, Browman 2003.…”

“…To determine the ecological relevance of the experimental doses and dose rates, the daily UV (290 to 350 nm, the wavelength range over which damage occurs) exposure of Calanus finmarchicus embryos was calculated using a simulation model (Kuhn et al 2000). The model was developed for water masses in the estuary and Gulf of St. Lawrence, and so is directly relevant, and applicable here.…”

“…All simulations were performed under extant ambient atmospheric ozone levels. For details of the model, see Kuhn et al (2000) In summary: the few studies examining reciprocity in crustacean zooplankton and ichthyoplankton have yielded contradictory results. In general, it appears that reciprocity holds mainly for organisms without a strong capacity for photo-repair.…”

Inhibition of Phytoplankton and Bacterial Productivity by Solar Radiation in the Ross Sea Polynya

“…However, estimates can be made using mathematical models. The quantitative response to UV exposure is characterized well enough for some processes that statements can be made about integrated effects over the water column as a function of vertical mixing in the surface layer (Neale et al, 1998;Huot et al, 2000;Kuhn et al, 2000). These model results, together with profi les of UV-specifi c effects like DNA damage under qualitatively different mixing conditions (Jeffrey et al, 1996b;Huot et al, 2000), argue that mixing signifi cantly modifi es water column effects (Neale et al, 2003).…”

Impact of ultraviolet radiation on marine crustacean zooplankton and ichthyoplankton:a synthesis of results from the estuary and Gulf of St. Lawrence, Canada

“…This result is consistent with the data presented above-C. finmarchicus eggs are more susceptible to UV-B radiation than are cod eggs. Complete details of the model, and the scenarios evaluated, are reported in Kuhn et al (2000).…”