Depth distributions of DNA damage in Antarctic marine phyto- and bacterioplankton exposed to summertime UV radiation

During a survey from January to March 1998, the occurrence of W-B radiation (UVBR)-induced DNA damage in Antarctic marine phytoplankton and bacteriopl ankton was investigated, Sampling was done in Ryder Bay, off the British ba se Rothera Station, 67 degreesS, 68 degreesW (British Antarctic Survey). Sa mples were taken regularly during the survey period at fixed depths, after which DNA damage was measured in various plankton size fractions: (> 10, 2- 10, and 0,2-2 mum). Incident solar radiation was measured using spectroradi ometry, whereas attenuation of biologically effective UVBR was studied usin g a DNA dosimeter, A diatom bloom was found in the bay during the research period, judging from microscopic observations and HPLC analyses of taxon-sp ecific pigments, The high phytoplankton biomass likely caused strong attenu ation of DNA effective UVBR (Kbd-eff). Kbd-eff values ranged from 0.83 .m(- 1) at the peak of the bloom to 0.47 .m(-1) at the end of the season. UVBR-m ediated DNA damage, as measured by cyclobutane pyrimidine dimer (CPD) abund ance, was detected in all plankton Size fractions, Highest levels were foun d in the smallest size fraction, mainly consisting of heterotrophic bacteri a. Clear CPD depth profiles were found during mid-summer (January, beginnin g of February) with surface levels exceeding 100 CPDs per million nucleotid es in the bacterioplankton fraction. At that time, melting of the continuou sly present shelf ice caused strong salinity gradients in the upper meters, thereby stimulating water column stabilization. At the end of February and beginning of March, this phenomenon was less pronounced or absent, At that time, DNA damage was homogeneously distributed over the first 10 m, rangin g between 20 and 30 CPDs per million nucleotides for the smallest size frac tion,