LAUSR

The effects of ecologically relevant concentrations of Irgarol 1051, a representative PSII herbicide, on hermatypic corals were studied in the laboratory. The colour and chlorophyll fluorescence of Acropora tenuis were examined following exposure to around ambient concentrations of Irgarol 1051 (20 ng/L and 200 ng/L) for 7 days. While the colour of corals was stable throughout the experiment at both concentrations, the maximum effective quantum yield (ΔF/Fm') of symbiotic dinoflagellates decreased with increasing Irgarol 1051 concentration (day 7: 8%, 20 ng/L; 37%, 200 ng/L). The expression of heat shock protein (HSP) 70 and 90 in symbiotic dinoflagellates was upregulated after 7 days exposure to both Irgarol concentrations, whereas HSP90 in coral was not upregulated. The findings of the present study suggest that the threshold of chlorophyll fluorescence and HSP expression in symbiotic dinoflagellates is lower than 20 ng/L, which is around ecologically relevant concentrations in tropical to subtropical waters.