Phytotoxicity induced in isolated zooxanthellae by herbicides extracted from Great Barrier Reef flood waters

► We sampled a flood plume in the Great Barrier Reef lagoon. ► Polar organic compounds including herbicides were extracted and dosed on zooxanthellae. ► Photosynthetic inhibition was measured at a range of concentration factors. ► Inhibition was observed at all sites apart from one at a concentration factor of 10. ► Observed inhibition was correlated with salinity and measured diuron concentration.