Modeling the
effects of ultraviolet radiation on embryos of Calanus finmarchicus and
Atlantic cod (Gadus morhua) in a mixing environment
P.S. Kuhn, H.I. Browman, F.R. Davis, J.J. Cullen,
B.L. McArthur-2000
Limnology and Oceanography, 45 (8) : 1797-1806
(from Current Contents)
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 WR. 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 similar to 99% over numerous environmental 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 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 held 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 dearest 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.
(Dalhousie Univ, Dept Oceanog, Halifax, NS B3H 4J1,
Canada)