Patterns and Sources of Variability in Biological Weighting Functions for UVR Inhibition of Primary Production in California Coastal Waters

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Significant changes in UVR climatology have occurred all latitudes, except the tropics, during the last 20 years with potentially significant consequences for coastal oceanography. There is a pressing need to understand and be able to forecast UVR effects on coastal primary production; in part because of the central role carbon fixation plays in ecosystem dynamics, in part because of the various but untested scenarios suggesting changes in production patterns in response to changing UVR climatology, and in part out of concern for the potential impact these scenarios might have on coastal societies. With prior NSF funding, we have documented that inhibition of marine primary production by solar ultraviolet radiation (UVR) is widespread in phytoplankton, macroalgae, epilithic microalgae and ice algae in the Southern Ocean. To advance the spectral modeling of solar UVR effects on primary production, we measured the first of several action spectra or biological weighting functions (BWFs) quantify the spectral sensitivity of primary production to UVR inhibition under natural field conditions. We documented, for the first time, the significant variability in these spectral algorithms and identified but have not tested potential experimental, analytical and natural sources of that variability. Such knowledge is required if the predictive linkages between optical models of UVR and UVR effects on primary production are to be known. Lack of consideration of UVR effects undermines the predictive accuracy of primary production models and overlooks the regulatory roles that UVR plays in modifying cell processes that define the photoecology of phytoplankton. It is likely that the nature of the UVR challenges may differ in different ecosystems and the interactive effects on food webs may be balanced differently. A feasibility study of surface phytoplankton communities in the Santa Barbara Channel during 1995 indicate a potential for significant, but highly variable, UVR effects on surface primary production rates. Based on those findings and using proven techniques, we will define the patterns and sources of variability in BWFs for UVR inhibition of primary production in highly diverse California coastal waters and, thereby, advance spectral modeling of UVR dependent primary production. The results of this research project will also help identify the mechanisms by which UVA and UVB regulate the polychromatic biology of phytoplankton and provide insights regarding potential consequences of changing global UVB climatology on phytoplankton ecology.