Experimental evidence for the cyanobacteria - mixotrophs succession in eutrophic lakes under extreme drought

COSTA, M. R. A.; MICELI GONÇALVES, H.; LACATIVA BAGATINI, I.; UNREIN, F.; BECKER, V.; SARMENTO, H.

Taller; 2do Taller de la Red colaborativa en Ecología Microbiana Acuática en América Latina (μSudAqua); 2019

Climate change is altering hydrological regimes, increasing water scarcity in lakes and reservoirs, especially in semi-arid regions. The drastic reduction of water volume sometimes enables sediment resuspension, which increases inorganic turbidity and reduces light availability in the water column. In this context, the ecosystem dynamics is altered, affecting biological communities, mainly primary producers that depend on light availability. Recent studies indicate that eutrophic environments usually dominated by cyanobacteria, may shift towards a domination of mixotrophic algae after drastic reduction of water volume, possibly as a response to the decrease in light availability. The aim of this study was to evaluate the effect of inorganic turbidity in the growth rates of a mixotrophic phytoflagellate and bloom forming cyanobacteria in laboratory experiments. To do so, cultures of cyanobacteria Microcystis aeruginosa Kützing and mixotrophic Cryptomonas obovata Czosnowski were grown axenically and non-axenically, in monocultures under different conditions of turbidity and light. We found that in treatments with sediment (high turbidity), mixotrophic species had higher growth rates than cyanobacteria only in treatments containing bacteria. This may be because Cryptomonas can change its nutritive strategy from autotrophy to heterotrophy or mixotrophy due light limiting conditions. Given the increasing water scarcity already observed in most semi-arid regions, this work seeks to elucidate the mechanisms of the cyanobacteria - mixotrophs succession in eutrophic lakes under extreme drought.