Picoplankton structure and productivity in environments with different light climates in a South American wetland.

IZAGUIRRE, IRINA; DE TEZANOS PINTO, PAULA; O'FARRELL, INES; RODRIGUEZ, PATRICIA LAURA; PIZARRO, HAYDEE; UNREIN, FERNANDO; GASOL, JOSEF

Montreal, Canadá

Congreso; 30 Congreso de la Asociación Internacional de Limnología aplicada y teórica; 2007

SIL

The autotrophic picoplankton (picocyanobacteria and picoeukaryotes) was seasonally analysed in water environments from a wetland of the Lower Paraná Basin (Otamendi National Reserve). The selected sites included two shallow lakes (littoral and pelagial) and relictual oxbow-lakes (ROLs) that are frequently covered by floating macrophytes. Picocyanobacteria (rich in ficocianine), dominated over picoeukaryotic algae (generally higher 80%). Total picoplankton densities along the year varied from 19,800  to 457,000 cells/ml in the shallow lakes, and 5,700 to 255,000 cells/ml in the ROLs. Changes in autotrophic and heterotrophic picoplankton in relation to light reduction due to floating plants were analysed experimentally using mesocosms; flow cytometry analyses revealed important changes in the picoplankton structure in relation to light. Mesocosms directly exposed to the light showed a higher proportion of pico-eukaryotic algae over picocyanobacteria; photosynthetic bacteria were found in mesocosms covered by floating plants. Primary production (PP) of the picoplankton was also analysed at the different sites. PP values were higher in summer for all the sites; important differences among the environments  were found, with very low PP values in the ROLs (13 to 35 ug C/L/ h), and the highest ones in the shallow lakes (38 to 470 ug C/ L/ h).