La luz y las comunidades planctónicas: existe un impacto significativo de parte de la Radiación Ultravioleta B en el ambiente natural?

FERREYRA, G. A.; SCHLOSS, I. R.; HERNANDO, M.; HERNÁNDEZ, E.; BOUCHARD, J.; OYARBIDE, F.; TOSONOTTO, G.; GONZÁLEZ, O.; CANTONI, L.; CURTOSI, A.; ULRICH, A.; RODRÍGUEZ, S. Y DEMERS, S.

Buenos Aires

Simposio; VI° Simposio Argentino y III° Latinoamericano sobre Investigaciones Antárticas; 2007

DNA-IAA

The main goal of this study was to understand the responses of Antarctic bacterioplankton and phytoplankton to UBVR in the water column. A 30-days time series high frequency (every 6 h) sampling was performed between February 11 and March 12 2002 at a fixed station located in the vicinity of the Argentinean station Melchior (64° 20’S, 62° 59’W). Biological parameters measured were: activity of the photosystem II (PSII), carbon assimilation by phytoplankton, chlorophyll a (Chl-a), photoprotection (D1 protein cycle and synthesis of mycosporine like amino-acids (MAAs)), phytoplankton composition and abundance, heterotrophic activity and abundance of total and viable bacterioplankton. Physical and chemical variables were simultaneously studied (structure of the water column, incident spectral irradiance and its penetration in the water column, tides, wind intensity and direction, and nutrients). Only part of the results are shown here. The whole sampling period was characterized by relatively low winds (< 4 m s-1), which allowed the development of a well developed pycnocline in the water column, with an upper mixed layer (UML) ranging between ~5 and ~35 m depth. The depth of the 1% of incident UVBR (Zeu UVBR) averaged ~15 m, while the same percent corresponding to ultraviolet A (UVAR, 315-400 nm) reached ~40 m depth (Zeu UVAR). Phytoplankton assemblages were numerically dominated by Cryptomonas-1), which allowed the development of a well developed pycnocline in the water column, with an upper mixed layer (UML) ranging between ~5 and ~35 m depth. The depth of the 1% of incident UVBR (Zeu UVBR) averaged ~15 m, while the same percent corresponding to ultraviolet A (UVAR, 315-400 nm) reached ~40 m depth (Zeu UVAR). Phytoplankton assemblages were numerically dominated by Cryptomonaseu UVBR) averaged ~15 m, while the same percent corresponding to ultraviolet A (UVAR, 315-400 nm) reached ~40 m depth (Zeu UVAR). Phytoplankton assemblages were numerically dominated by Cryptomonas) averaged ~15 m, while the same percent corresponding to ultraviolet A (UVAR, 315-400 nm) reached ~40 m depth (Zeu UVAR). Phytoplankton assemblages were numerically dominated by Cryptomonaseu UVAR). Phytoplankton assemblages were numerically dominated by Cryptomonas). Phytoplankton assemblages were numerically dominated by Cryptomonas sp. and small flagellates < 5 μm, followed in abundance by diatoms. Cells were exposed to UVBR a significant part of the time while most of the time they were exposed to UVAR. This high degree of exposure resulted in significant effects of these radiations on physiological (PSII and carbon assimilation and Chl-a per cell) and state (biomass) parameters, which showed to strongly relate with the time of the day and on irradiance intensity. Photoprotective mechanisms (de novo synthesis of D1 protein and synthesis of MAAs) showed a rapid reaction to increased levels of irradiance. Both the abundance and the ratio of viable to total VI SIMPOSIO ARGENTINO Y III LATINOAMERICANO SOBRE INVESTIGACIONES ANTÁRTICAS - VI ARGENTINE AND III LATIN-AMERICAN SYMPOSIUM ON ANTARCTIC RESEARCH Dirección Nacional del Antártico / Instituto Antártico Argentino - 10 al 14 de Septiembre de 2007 - 10th to 14th September, 2007th to 14th September, 2007 bacterioplankton decreased under higher exposure. However, heterotrophic activity showed an opposite trend, probably related to an increased availability of dissolved organic carbon from cell death. Since this study is still underway, no conclusions can be derived so far. However, a significant finding of this research was that ultraviolet radiation not only affected key components of the plankton community like bacterioplankton and phytoplankton in their natural environment, but also interactions between them. Further analyses are necessary to complete the interpretations of these results.