BALSEIRO esteban Gabriel
congresos y reuniones científicas
Light and resource supplies as factors modulating niche partitioning in two pelagic mixotrophic ciliates
MODENUTTI, BE; ESTEBAN GABRIEL BALSEIRO, ESTEBAN G. BALSEIRO, BALSEIRO, E.G; CALLIERI, C.; BERTONI, R.
Congreso; SEFS-5; 2007
Lake stratification enhance light supply through a decrease in mixing depth, while extended epilimnetic layers imply shortage of light, because planktonic producers are frequently dragged down to low light levels. Similarly, mixotrophic ciliate species can be affected by changes in light availability by a direct effect on the endosymbiotic algae. Nevertheless, mixotrophic ciliates can eat either bacteria or other protists and, consequently, be also affected by prey availability. Planktonic photosynthetic biomass of Andean Patagonian lakes is dominated by two mixotrophic ciliates, Stentor araucanus and Ophrydium sp. We examined in the oligotrophic Lake Moreno their population during two contrasting summer seasons (strong vs mild windy years), postulating the thermocline depth and light availability as factors that would determine the relative abundance of these species. Additionally, we studied bacteria inside food vacuoles with the CARD-FISH technique in order to assess differences in prey ingestion. S. araucanus, a resistant species to UVR, was present in the epilimnion attaining higher abundances when the thermocline depth was lower and the mean irradiance higher. On the contrary, Ophrydium, showed an opposite pattern preferring the metalimnetic layers and being more abundant with deeper thermoclines. We observed that food niche overlap was negligible. Ophrydium grazed on all the bacteria assemblage including archea and picocyanobacteria. On the contrary, we did not identify bacteria on food vacuoles of Stentor araucanus suggesting that small particles are eaten a very low proportion. The analysis of photosynthetic efficiency showed that Ophrydium is efficient at low light intensities. The large and dark S. araucanus needs a high light supply to maintain endosymbiotic algal photosynthesis showing a sharp decrease in efficiency below 100 µmol photons m-2 s-1. Our results suggested that the temporal or spatial variation in thermoclines depth would imply advantages for one or other ciliate species.