Abstract
Coral bleaching due to global warming currently is the largest threat to coral reefs, which may be exacerbated by altered water quality. Elevated levels of the UV filter oxybenzone in coastal waters as a result of sunscreen use have recently been demonstrated. We studied the effect of chronic oxybenzone exposure and elevated water temperature on coral health. Microcolonies of Stylophora pistillata and Acropora tenuis were cultured in 20 flow-through aquaria, of which 10 were exposed to oxybenzone at a field-relevant concentration of ~0.06 μg L−1 at 26 °C. After two weeks, half of the corals experienced a heat wave culminating at 33 °C. All S. pistillata colonies survived the heat wave, although heat reduced growth and zooxanthellae density, irrespective of oxybenzone. Acropora tenuis survival decreased to 0% at 32 °C, and oxybenzone accelerated mortality. Oxybenzone and heat significantly impacted 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. Our results suggest that oxybenzone adds insult to injury by further weakening corals in the face of global warming.
Highlights
Coral bleaching due to global warming is currently the largest threat to tropical coral reefs (Hughes et al, 2017)
Measured oxybenzone concentrations were 0.05 ± 0.03 μg L−1 for the 26 °C aquaria and 0.06 ± 0.05 μg L−1 for Combined exposure to oxybenzone and elevated temperature accelerated mortality in A. tenuis with 2 days compared to temperature elevation alone (Fig. 3)
None of the oxybenzoneexposed A. tenuis colonies survived at 31.5 °C, whereas the control colonies all died at 32 °C
Summary
Coral bleaching due to global warming is currently the largest threat to tropical coral reefs (Hughes et al, 2017). Wooldridge and Done (2009) showed that corals growing in nutrient-enriched coastal waters had a decreased bleaching resistance compared to reefs in oligotrophic oceanic waters. Herbicide levels were not field-relevant, Amid et al (2018) observed combined effects of elevated temperature and herbicides on the photosynthetic capacity of Acropora formosa, indicating the relevance of studying multiple stressors simultaneously. These studies provide several examples of additive stress resulting in coral bleaching, research on the combined effects of water quality and water temperature on coral health remains limited (Ban et al, 2014)
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