UV effects on marine production by bacteria and phytoplankton: Assessing the impact of UVB Principal Investigator: Wade H. Jeffrey, PhD Co-principal Investigator: Patrick Neale, PhD. Smithsonian Environmental Research Center, Edgewater, MD Support Agency: National Science Foundation Location of Study: Gulf of Mexico, Chesapeake Bay

Ultraviolet radiation (UVR, 290-400 nm) from the sun penetrates to significant depths in many marine environments and a variety of studies have indicated its ecological importance. Stratospheric ozone depletion is changing the spectral composition of solar UVR to varying degrees in different locations by increasing levels of biologically harmful, short wavelength UVB (290-320 nm). Previous work has shown that both UVB and the longer wavelength UVA (320-400 nm) affect marine carbon cycling, primarily through effects on phytoplankton and bacterioplankton which comprise the base of oceanic food webs. While phytoplankton are responsible for carbon fixation, bacterioplankton play a vital role in the mineralization of nutrients and provide a trophic link to higher organisms. Assessing the impact of UV on these processes during variations in ozone and water transparency requires accurate knowledge of spectral dependence. This dependence is described by a biological weighting function (BWF). Significant effort has been devoted in the last two decades to resolving BWFs for biological processes controlling rates of primary production in aquatic environments (i.e. photoinhibition). Compared to reports of UV effects on phytoplankton, however, studies of the impact and effects of UVR on bacterioplankton are in their relative infancy. Previous work with bacterioplankton has been limited to broad spectrum analysis (i.e. UVA vs UVB). Unfortunately, such limited spectral resolution precludes prediction, particularly of the effects of increased UVB due to ozone depletion. The principal goal of this project is to develop biological weighting functions for inhibition of bacterioplankton production using DNA, RNA, and protein synthesis as representative biological processes. Biological weighting functions will be determined for diverse marine environments (Chesapeake Bay and Gulf of Mexico) using polychromatic light regimes and compared to similar functions measured for phytoplankton. Models will be developed and compared to in situ measurements of production and examined for significant disparities. This study will increase our understanding of the spectral sensitivity of natural assemblages of bacterioplankton in diverse environments and of the role of UVR in controlling marine ecosystems with particular reference to increased UVB associated with stratospheric ozone depletion.