Phytoplankton acclimation and spectral penetration of UV irradiance off the central Chilean coast

Abstract

This study of surface and underwater UV irrad~ance and its effect on phytoplankton photosynthesis was carried out in autumn, winter and spring at coastal and oceanic stations off the coast of central Chile (30 end 33 S ) . At S during autumn, l % of surface UVB irradiance (308 nm) reached a minimum depth (Zuv,,) of 11 m and a maximum depth of 15 m without a significant difference between coastal and oceanic areas. In winter, the Zuvaoamn minimum was 15 m within 80 km offshore (coastal stations) and the ZUV30Bnm maxlmum was 17 m at the oceanic station. 200 km offshore. UVA (ZVV380nm) reached a minimum of 24 m and a maximum of 4 2 m in autumn, also with no significant spatial trend. In winter, 1 % of this spectral band reached a depth of 32 to 36 m at the coastal stations (within 80 km) and 50 m at the oceanic station. Photosynthesis (P) versus irradiance (l) experiments carried out on deck, with and without UV irradiance, showed no significant differences in maximum specific photosynthesis (P&,,). It was also found that on a scale of hours, the microalgae were able to increase the absorbance ratio 330-340/665 nm. In vitro during 2 h incubation under constant photosynthetically available radiation (PAR) plus 10 different levels of UVB, PB,,, was significantly inhibited (>10%) at a 305 nm dosage rate of 1 pW cm-' nm-' Nevertheless, this amount of UVB never reached deeper than 3 m into the water column during the period studied at 30 ' s . These results suggest that under severe ozone depletion only the upper fraction of the euphotic zone would be under higher UV irradiances and, given an appropriate time (hours) to acclimatize, phytoplankton will be able to cope with this environmental stress. K E Y WORDS: Upwelling Chile-Peru Eastern Boundary Current . UV-absorbing compounds