Photosynthetic activity under UVR exposure and nutrient addition of phytoplankton from coastal sites off São Francisco do Sul, Santa Catarina (Southern Brazil)

ERZINGER, G. S.; VILLAFAÑE, V. E.; STRAUCH, S. M.; MACHADO, C. K.; HELBLING, E.W

Montreal

Congreso; 36th meeting of the American Society for Photobiology; 2012

American Society for Photobiology

During March 2011 we carried out experiments to evaluate the photosynthetic activity of phytoplankton collected from the area of São Francisco do Sul, Santa Catarina, Brazil, when exposed to solar radiation and nutrient addition. We collected samples from the following sites: a) Prainha; b) Ubatuba; c) Babitonga Bay (both from the mouth and inlet waters) and exposed them to three radiation conditions (PAB, 280-700 nm; PA, 320-700 nm and P, 400-700 nm, using cut-off filters) throughout a daylight exposure; two nutrient treatments were implemented: Addition of f/2 medium the night previous of experimentation vs. natural concentration. Every 30-60 min measurements of various chlorophyll a (Chl a) fluorescence parameters were done using a PAM fluorometer. At all sites, there were significant effects of the different wavebands, as seen in the reduction of the photochemical quantum yield (Y) values, especially in samples under the PAB treatment. Nutrient addition however, was by far more important in counteracting the UVR impact by increasing Y significantly as compared to samples under natural nutrient levels. In spite of these general patterns of photosynthetic responses under the treatments implemented, there was important variability among the sites sampled. For example, while at Prainha there was a rather smooth decrease of Y towards noon and partially recover in the afternoon, samples from Ubatuba displayed variable responses, generally following radiation patterns, but in any case, samples recovered only partially or did not recover at all during afternoon hours. Samples from the mouth and inlet waters of Babitonga Bay had similar photosynthetic responses (i.e., with a significant decrease of Y towards noon and recovery in the afternoon). However, samples from the inlet recovered faster and more complete than those from the mouth. These variable responses among sites may be attributed not only to the different radiation conditions throughout the experimental period (which ranged in average from 0.33-1.17, 12.9-40.6 and 113-287 W m-2 for UV-B, UV-A and PAR, respectively), but also to the differential taxonomic composition of the communities sampled: Diatoms dominated at Prainha and Ubatuba (i.e., Asterionellopsis glacialis) whereas at the mouth of Babitonga Bay dominated Leptocylindrus sp.; however, at the inlet unidentified pico-nanoplankton flagellates were the most abundant group.