AME 65:221-232 (2012)  -  DOI:

Grazing rates of protists in wetlands under contrasting light conditions due to floating plants

Irina Izaguirre1,*, Rodrigo Sinistro1, M. Romina Schiaffino1, María Laura Sánchez1, Fernando Unrein2, Ramon Massana3

1Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales—CONICET. Ciudad Universitaria, C1428EHA, Buenos Aires, Argentina
2IIB-INTECH (Instituto de Investigaciones Biotecnológicas—Instituto Tecnológico de Chascomús)—CONICET. 7130, Chascomús, Argentina
3Institut de Ciències del Mar-CSIC, 08003 Barcelona, Spain

ABSTRACT: We examined the effect of light attenuation, due to floating plants, on the community structure of the main phagotrophic protists and their grazing rates in a wetland in the Lower Paraná Basin. Ingestion experiments (winter and summer) were conducted at 2 sites in the same shallow lake that had contrasting light scenarios: open waters (light) and under profuse macrophyte coverage (dark: light attenuation ~97%). We compared the rates at which protists ingested 3 types of tracer prey: fluorescently labelled heterotrophic bacteria (FLB), picocyanobacteria (FLC) and picoeukaryotic algae (FLA). Light influenced both the structure of the microbial communities and the protistan grazing rates. Heterotrophic flagellates (HF) were more abundant under the macrophytes, whereas mixotrophic algae (cryptophytes) and autotrophic and heterotrophic picoplankton populations attained higher abundances in open waters. Specific grazing rates (SGRs) of mixotrophs on heterotrophic bacteria (HB) were higher in the light (7.9 to 15.5 prey cells grazer−1 h−1), than in darkness (0.1 to 5.1 prey cells grazer−1 h−1); the same trend was observed on picocyanobacteria (Pcy) (1.1 and 0.2 prey cells grazer−1 h−1, light and dark). SGRs of HF were 1.0 to 7.3 cells grazer−1 h−1 (on HB) and 0.01 to 1.8 prey cells grazer−1 h−1 (on Pcy), with highest values in summer and no pattern in relation to light. SGRs of ciliates were higher in summer and in darkness. Clearance rates (CR) on Pcy were higher than on HB, for both HF and mixotrophic algae. In winter, cryptophytes contributed up to 93% of the microbial grazing in the light, whereas HF were more important in darkness; in summer, bacterivory was dominated by heterotrophs in both light scenarios. Our experimental results highlight the importance of light conditions in structuring bacterial grazing by protists.

KEY WORDS: Phagotrophy · Protists · Mixotrophic algae · Grazing rates · Wetland · Light ­attenuation

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Cite this article as: Izaguirre I, Sinistro R, Schiaffino MR, Sánchez ML, Unrein F, Massana R (2012) Grazing rates of protists in wetlands under contrasting light conditions due to floating plants. Aquat Microb Ecol 65:221-232.

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