Preliminary data on chronic effects of ultraviolet radiation on the growthof some phytoplankton species of the Beagle Channel, Argentina

Serious concerns exist that the thinning of stratospheric ozone and the res ulting enhancement in the solar UVB radiation, may impair marine primary pr oductivity. Also, UVB may alter food web dynamics and food availability for high er trophic levels in marine ecosystems inducing changes in phytoplank ton species composition. The main goal of this study was to examine the res ponses of different species of marine phytoplankton to solar UVR. Specifica lly, we compared the UV sensitivity of a phytoplankton natural community is olated from the Beagle Channel (54 degrees 52'S, 68 degrees 18'W, Ushuaia, Argentina). as well as the response of two taxa which were isolated from th at community (i.e., a pennate diatom, Navicula sp., and a phytoflagellate p ertaining to the Class Cryptophyceae) to UV radiation. Exposure to UVB or U VA radiation treatments had no significant effects (p>0.05) on exponential growth rate in Navicula sp However, when the phytoflagellate [Class Cryptop hyceae] was exposed to UVB, the growth rate in the exponential phase was in hibited significantly (p<0.01) compared with the PAR control. Marked change s in the relative abundance of the main taxonomic groups were observed in t he community cultures: the relative abundance of phytoflagellates was signi ficantly lower after exposure to the UVB treatment than after exposure to t he PAR treatment (p<0.05). However, the percentage of centric diatoms incre ased significantly (p<0.05) when they were exposed to UVB. The growth rate at the end of the exponential phase of growth of the community was inhibite d significantly (p<0.01) when the algae were exposed to UVB and UVA.