Adding insult to injury: The effects of chronic oxybenzone exposure and elevated temperature on two reef-building corals

We studied the combination effect of chronic oxybenzone exposure and elevated temperature on coral health. Microcolonies of Stylophora pistillata and Acropora tenuis were cultured in flow-through aquaria, with or without oxybenzone at a field-relevant concentration of ~0.06 μg L-1 at 26 °C. After two weeks, half the corals experienced a heat wave culminating at 33 °C. All S. pistillata colonies survived, with reduced growth and zooxanthellae density during the heat wave, irrespective of oxybenzone. A. tenuis survival was reduced to 0% at 32 °C, and oxybenzone accelerated mortality. Oxybenzone and the heat wave reduced photosynthetic yield in both species, causing a 5% and 22-33% decrease, respectively. In addition, combined oxybenzone and temperature stress altered the abundance of five bacterial families in the microbiome of S. pistillata, suggesting reduced resilience. Our results suggest that oxybenzone adds insult to injury by further weakening corals in the face of climate change.