Expression analyses of stress-responsive genes in the hermatypic coral Acropora tenuis and its symbiotic dinoflagellates after exposure to the herbicide Diuron

Concentration of Two Herbicides, Irgarol 1051 and Diuron, in Coastal Waters of Coral Reefs and Adjacent Waters in the Northwestern Part of Okinawa Island, Japan

Irgarol 1051 and Diuron are used as boosters in copper-based anti-fouling paints, as well as in agriculture and home gardening. We monitored the coral reefs and adjacent waters of northern Okinawa Island three times, i.e., in August 2015, June 2016 and December 2016. The mean concentrations were 1.44 ng/L for Irgarol and 1.07 ng/L for Diuron. Although the range of these concentrations was lower than those previously recorded in southern Japan, Irgarol and Diuron were significantly higher in December 2016 than in June 2016. Several estimations of Predicted No Effect Concentrations (PNECs) have recently been published. In December 2016, compared to the lowest PNEC concentration of each substances, the concentrations of Irgarol and Diuron exceeded the PNEC at nine sites and three sites, respectively. These results suggest that the effects of low concentrations of Irgarol and Diuron, close to the PNEC, on hermatypic corals need to be investigated. The regulation of anti-fouling paints in Japan is self-regulated through industry cooperation. Irgarol and Diuron have not been registered as anti-fouling paints for fishing nets by the fishing cooperatives. The significant increase of these substances suggests that the activity of vessels with paints containing Irgarol has increased in December 2016. This study highlights the need for continuous monitoring of these herbicides in coral reefs and adjacent waters.

Transcriptome analysis reveals limited toxic effects of the UV-filter benzophenone-3 (BP-3) on the hermatypic coral Acropora tenuis and its symbiotic dinoflagellates

This study aimed to investigate the toxic and transcriptomic effects of the ultraviolet filter benzophenone-3 (BP-3) on Acropora tenuis and its symbiotic dinoflagellates while using acetone as a solvent. Seven-day exposure to 50 and 500 μg/L, which is higher than most BP-3 records from coastal waters, did not affect coral colour or dinoflagellate photosynthesis. Differentially expressed genes (DEGs) between seawater and solvent controls were <20 in both corals and dinoflagellates. Eleven coral DEGs were detected after treatment with 50 μg/L BP-3. Fourteen coral DEGs, including several fluorescent protein genes, were detected after treatment with 500 μg/L BP-3. In contrast, no dinoflagellate DEGs were detected in the BP-3 treatment group. These results suggest that the effects of 50-500 μg/L BP-3 on adult A. tenuis and its dinoflagellates are limited. Our experimental methods with lower acetone toxicity provide a basis for establishing standard ecotoxicity tests for corals.