Combined effects of climate change and the herbicide diuron on the coral Acropora millepora

The Great Barrier Reef (GBR) is threatened by climate change and local pressures, including contaminants in nearshore habitats. This study investigated the combined effects of a GBR-relevant contaminant, the herbicide diuron, under current and two future climate scenarios on the coral Acropora millepora. All physiological responses tested (effective quantum yield (ΔF/Fm'), photosynthesis, calcification rate) were negatively affected with increasing concentrations of diuron. Interactive effects between diuron and climate were observed for all responses; however, climate had no significant effect on ΔF/Fm' or calcification rates. Photosynthesis was negatively affected as the climate scenarios were adjusted from ambient (28.1 °C, pCO₂ = 397 ppm) to RCP8.5 2050 (29.1 °C, pCO₂ = 680 ppm) and 2100 (30.2 °C, pCO₂ = 858 ppm) with EC50 values declining from 19.4 to 10.6 and 2.6 μg L^-1 diuron in turn. These results highlight the likelihood that water quality guideline values may need to be adjusted as the climate changes.