Light, Mixing Depth and Bacterivory by Mixotrophic Protists in Andean North-Patagonian Lakes

MODENUTTI B.; BASTIDAS NAVARRO M.; BALSEIRO E.

Córdoba

Congreso; 16th International Congress of Photobiology; 2014

Light, nutrients, mixing intensity and mixing depth are environmental factors that have a large effect on the ecological dynamics of plankton. Although plankton communities are generally suspended in a well-mixed medium, within aquatic ecosystems light may have a complex pattern of spatial and temporal variability. Vertical mixing can lead to a shortage of light if planktonic organisms are frequently mixed down to the bottom, whereas stratification enhances light supply by decreasing mixing depth. North Patagonian Andean lakes from Argentina are high light/low nutrient environments, in which mixotrophy appears as a suitable and very common strategy for exploiting the extended euphotic zone of the water column. Here we present an analysis of different field and laboratory bacterivory experiments carried out under different light treatments. Bacterivory was assessed in protists (nanoflagellates and ciliates) by computing fluorescently labeled bacteria (FLB) inside the feeding vacuoles. Results show that ultraviolet radiation (UVR) reduced bacterivory although the negative effect was more evident in mixotrophic nanoflagellates in comparison with heterotrophic ones. Protists consumption rate on bacteria was observed to be reduced up to approximately 70-77 % by UVR. Finally, we show that carbon transfer in the microbial food web would be substantially altered by different temporal heterogeneity in vertical mixing including the UVR effect.