"Effect of rainbow trout introductions on food webs in lakes of the arid Patagonia

MARÍA SOL, PORCEL; FOGEL MARYLIN; IRINA IZAGUIRRE; IGNACIO, ROESLER; JULIO LANCELOTTI

Natal

Congreso; International Shallow lakes conference; 2022

Shallow lakes

This study focused on the analysis of the limnological changes associated to water level fluctuations in two shallow lakes (Cervecero and Chapu) of the Buenos Aires plateau, and the effects on their planktonic communities. In 2015, these two lakes were in a clear-vegetated state, being more suitable for waterbird nesting. In 2016, the water level was dropped by half (aprox.1m), in 2017 lakes dried completed, and next year, lakes were filled again due to winter snowfall. Environmental and plankton samples were collected in three summer campaigns (2015, 2016 and 2018) to answer, “how lakes change their abiotic characteristics and their planktonic communities with interannual hydrological variations”. Phyto- and zooplankton were analyzed by microscopy, while picoplankton assemblages were studied by flow cytometry and molecular techniques. Principal component analysis ordinated samples of 2016 towards higher values of dissolved organic carbon, total nutrients, and conductivity. Samples of 2015 and 2018 were ordinated with lower values of these variables. In 2015 and 2016, both lakes showed similar patterns of bacteria, the most abundant phyla were Proteobacteria and Bacteroidota. However, both lakes showed higher bacteria concentrations in 2016 than 2015. In 2018, Chapu presented 96% of Proteobacteria, while Cervecero showed 52% of Verrucomicrobiota. Photosynthetic picoplankton showed the highest concentration in 2018 dominating phycocyanin-rich picocyanobacterial in both lakes. Regarding phytoplankton, both lakes showed high diversity groups in 2015. In 2016, diatoms and chlorophytes dominated in Chapu and chlorophytes dominated in Cervecero. In 2018, chlorophytes dominated in Chapu and the cyanobacteria Dolichospermum flos-aque developed a bloom in Cervecero. Zooplankton also showed interannual variations in both lakes; particularly in 2018, Keratella kostei dominated in Cervecero, while in Chapu the groups were even. This study showed that the structure of the plankton communities markedly varies with interannual hydrological shifts, which has important implications for the conservation of these ecosystems.