Effects of ultraviolet radiation on the lower levels of the planktonic food web in Antarctica

FERREYRA, G., DEMERS, S., SCHLOSS, I., TOSONOTTO, G., HERNANDO, M., HERNANDEZ, E., OYARBIDE, F., CALVIÑO, E., RODRIGUEZ, S., CANTONI, L., GONZALEZ, O., ULRICH, A.

Buenos Aires, Argentina

Simposio; V° Simposio Argentino y I° Latinoamericano sobre Investigaciones Antárticas; 2004

DNA

Most of the studies that investigated the effects of ultraviolet radiation (UVR, 280-400 NM) on the first levels of the marine food web used experimental approaches (in situin situ incubations, micro and mesocosms). However, research on the responses to UVR of the microcommunity in their natural environment is scarce. A time series study including most of the oceanographic parameters described as controlling bacteria and phytoplankton dynamics was carried out (PAR, tidal mixing, turbulent mixing by winds and currents, nutrient stress). In this case, however, the effects of ultraviolet A and B (UVB, 280-320 nm and UVA, 320-400 nm, respectively) were added as forcing parameters. Fieldwork was done in the vicinity of Melchior Station (64° 20’S, 62° 59’W, Observatory Island). It involved the automated measurement of physical variables (currents, tides and meteorological data), as well as discrete sampling of physical (salinity, temperature), chemical (macronutrients) and biological variables (bacterial and phytoplankton abundance and production, PSII system, photoprotective compounds). Sub-surface sampling (0.5 m depth) was conducted with 5 L Niskin bottles at a fixed station (sampling every 6/12 h centered at local noon during the whole study period), and vertical profiles at 6 fixed depths (0, 5, 10, 20, 30 and 50 m) were done every four days. The whole study lasted for one month, from February 11 to March 12 2002. Average upper mixed layer (UML) was around 20 m and the depth of the euphotic zone (1% of incident radiation) for UVB and UVA was respectively 17 and 32 m, suggesting a strong influence of UVR on cells within the UML. PSII activity showed a significant inverse correlation with UVB, phased with irradiance oscillations. Bacterioplankton and phytoplankton biomass and production of both presented a similar response, but minimum values were lagged by 4-6 h from UVR maxima. Mycosporine like aminoacids (MAA’s) were also phased and directly correlated with UVR. The rest of the forcing parameters studied showed a minor influence on bacterioplankton and phytoplankton variability, thus suggesting that UVR may play a signficant role controlling their dynamics.