Plankton dynamics and photosynthesis responses in a eutrophic lake of Patagonia (Argentina): Influence of grazers abundance and UVR.

GONÇALVES, R.J.; VILLAFAÑE, V.E.; MEDINA, C.D.; BARBIERI, E.S.; HELBLING, E.W.

LATIN AMERICAN JOURNAL OF AQUATIC RESEARCH

UNIV CATOLICA DE VALPARAISO

Año: 2011 vol. 39 p. 117 - 130

0718-560X

Natural plankton populations from the eutrophic lake Cacique Chiquichano in Patagonia (Argentina) were monitored during one year to evaluate the changes in photosynthetic parameters of phytoplankton as a result of ultraviolet radiation (UVR, 280-400 nm) exposure, grazer abundance and taxonomic composition of the phytoplankton community. Variables, both physical (temperature, solar radiation) and biological (grazers, taxonomic composition, photosynthetic parameters) fluctuated throughout the study. Crustacean zooplankton showed alternated dominance between a cladoceran (Daphnia spinulata) and a copepod (Metacyclops mendocinus). Accordingly, phytoplankton community varied throughout the year, with cyanobacteria and diatoms alternating in their dominance. In addition, while copepods abundance was not significantly related to changes in phytoplankton, the presence of D. spinulata significantly gave place to clear water periods during which diatoms dominated. On the other hand, during periods of reduced penetration of solar radiation into the water column, cyanobacteria dominated the phytoplankton assemblage. Photosynthetic inhibition due to UVR decreased during the diatom dominated periods. In contrast, inhibition increased with increasing proportion of cyanobacteria, likely as a result of acclimation to low irradiances during the ’low transparency‘ phase of the lake. Moreover, D. spinulata presence was associated with increased penetration of solar radiation and thus indirectly increased the inhibition of cyanobacteria photosynthesis. Our results suggest that both solar radiation and grazing abundance have a strong influence in shaping and conditioning phytoplankton dynamics and photosynthetic responses in Lake Cacique Chiquichano.