A multi-stressor environment impairs the photosynthetic performance of Virescentia viride-brasiliensis (Batrachospermales, Rhodophyta)

Red algae belonging to Batrachospermales are important contributors to the energy input of lotic ecosystems. Given the importance of these algae for the lotic food web, we tested the photosynthetic performance of a relatively widespread and sensitive species (Virescentia viride-brasiliensis) in multi-stressor scenarios. Experiments were performed by exposing algal samples to three nominal concentrations (0.05 mg/L, 0.6 mg/L, and 1.2 mg/L) of tebuthiuron, a commonly used pesticide in Brazil, combined with three projected temperatures due to climate change (21.6ºC, 23.9ºC, and 26ºC). We observed a decrease in photosynthetic yield (Y(II)), regulated energy dissipation (Y(NPQ)), net photosynthetic rate (NPR), and dark respiration rate (DRR), while an increase in non-regulated energy dissipation (Y(NO)) was recorded, all of which indicate stress responses. Furthermore, we observed a dose-dependence relationship in which the negative effects increased with increasing tebuthiuron concentrations and in the scenario with a more severe temperature increase (26ºC). The high sensitivity of V. viride-brasiliensis to tebuthiuron highlights its potential bioindicator status because the tebuthiuron concentration accepted as safe for drinking water (0.05 mg/L) was sufficient to decrease its photosynthetic yield. Ultimately, these results show the importance of managing pesticide usage, especially considering the simultaneous occurrence of global warming.