Can Your Sunscreen Be Harming Coral Reefs?

It's a well known fact that wearing sunscreen is good for you. Whether it is preventing painful sunburns or skin cancer, sunscreen is an essential for many people. However, this innocuous product can potentially destroy coral reefs by affecting their health in several ways.

In a study published by Danovaro et. al. in 2008, sunscreen chemicals were found to cause rapid bleaching of hard corals by the induction of viruses that target the symbiotic zooxanthellae living on the corals. Coral bleaching occurs after a disturbance causes a coral colony to expel the zooxanthellae that live with it. Although this doesn't kill the coral, the colony becomes much more susceptible to disturbances and mortality.

Sunscreen gets into the environment by washing off of people's bodies when they swim, snorkel, or otherwise submerge in the water. Sunscreen concentrations are especially high in areas with a lot of tourism, and has become such a problem that some areas ban tourists from wearing sunscreen. The authors of this study estimated that some where between 4,000 to 6,000 tons of sunscreen enter the oceans each year, threatening around 10% of coral reefs to chemical bleaching.

Sunscreen contains a multitude of chemicals; one being parabens. Parabens are slowly being removed from personal care products because they have estrogenic qualities, so it's not surprising that such a compound would be harmful to marine life as well. Along with parabens, butylparaben, ethylhexylmethoxycinnamate, benzophenone-3 and 4-methylbenzylidene camphor caused complete bleaching of hard corals, even at very small doses. Whether a coral bleached or not was not concentration dependent, however, the rates of bleaching increased as concentrations of these chemicals increased. Sunscreens contain other chemicals besides these, but they were shown to have little to no effect on coral bleaching. The bleaching effect is caused by the release of viruses from the corals and zooxanthellae into the water surrounding the corals. This phenomenon was only observed with the exposed corals and not the controls, suggesting that the chemicals stimulate the viral expulsion.

Impact of sunscreen addition on nubbins of Acropora.
Untreated (brown) and treated (bleached)
 nubbins of (A) Acropora cervicornis (Caribbean Sea, Mexico); (B)
 Acropora divaricata (Celebes Sea, Indonesia);
(C) Acropora sp. (Red Sea, Egypt); and (D) Acropora ...

But, how do you go about measuring coral bleaching? One method is to quantify the bleaching by performing colorimetric analysis on digital photographs of the corals before and after the experiment. The effect of the chemical on coral bleaching is calculated by taking the difference between the color value given for the coral before the study and the color value of the coral after the study. The significance of the difference was taken using an ANOVA one-way analysis of variance test. With each chemical isolated, this test allowed the authors to determine which chemicals bleached corals and which had little or no effect.

This study, cited over 200 times, suggests that chemicals in sunscreen can cause coral bleaching. However, the authors did claim that the levels of chemicals were likely higher than those seen in the environment. Because coral bleaching occurred at such low doses and was not concentration dependent, it is likely that the same effects would be seen in the environment. Overall, tourists need to be conscious of their sunscreen use and how their activities are affecting the marine life. People should avoid wearing sunscreen when visiting coral reefs or choose sunscreens that are free of cinnamtes, camphor derivatives, parabens, and benzophenones. Recognizing how we impact the surrounding wildlife is important for the health of the environment. Studies like Danovaro et. al. bring to light how a seemingly safe product like sunscreen could actually be harmful.

Danovaro, R., Bongiorni, L., Corinaldesi, C., Giovannelli, D., Damiani, E., Astolfi, P., … Pusceddu, A. (2008). Sunscreens Cause Coral Bleaching by Promoting Viral Infections. Environmental Health Perspectives, 116(4), 441–447. http://doi.org/10.1289/ehp.10966