Effects of UV on photosynthesis of Antarctic phytoplankton: models and their application to coastal and pelagic assemblages

Abstract

We have characterized the photosynthetic response to ultraviolet= radiation (UV) of natural phytoplankton assemblages in Antarctic (Southern= Ocean) waters, Biological weighting functions (BWFs) and exposure response= curves for inhibition of photosynthesis by UV were measured during= spring-time ozone depletion (October-November). Two different models were= developed to relate photosynthesis to UV exposure. A model that is a= function of the duration of exposure (BWFH) applied to assemblages in the= well-mixed open waters of the Weddell-Scotia Confluence (WSC, 60 degrees S,= 50 degrees W), since responses were a function of cumulative exposure and= recovery rates were slow. These assemblages had a variable but generally= high sensitivity to UV. A steady-state model (BWFE) applied in the shallow= waters near the Antarctic Peninsula (Palmer Station, 64 degrees S, 64= degrees W), where inhibition was a function of irradiance (reciprocity= failed), and recovery was rapid. Using information on the time-dependence= of photosynthesis in assemblages with active repair. inferences were drawn= on the relative contribution of damage and recovery processes to the UV= weights. BWFs for Palmer phytoplankton sampled during periods of pack-ice= cover had both higher damage and higher repair than BWFs for WSC= assemblages. BWFs for Palmer phytoplankton sampled during open water= periods had about the same damage weights as Weddell-Scotia assemblages but= had a higher repair rate. Solar exposures of more than 10 min were= predicted to have generally less effect on Palmer phytoplankton than the= WSC phytoplankton.