Sunscreens: A culprit in widespread coral bleaching?

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By: Julia Zeh

When you put on sunscreen at the beach and then jump in the water, have you ever seen what looks like an oil slick appear in the water behind you? It turns out that sunscreen is not really all that waterproof, and it tends to come off when you go into the water. It’s not something that too many people notice or really begin to feel concerned about, but it just so happens that this small, sunscreen-induced oil slick actually has a negative impact on ocean life. Furthermore, components of sunscreen are found in noticeable quantities in areas around coral reefs. It may sound odd, but sunscreen can cause coral bleaching. The lotion you put on before you go swimming causes the loss of pigment and the eventual death of valuable marine organisms.

Coral is very important because it is the foundation of the marine ecosystem; the lives of marine organisms depend on coral. Coral reefs are the home of rich biodiversity, and when something happens that impacts coral, the entire ecosystem that is based in that reef is impacted as well. We must protect our reefs because they are so important to many animals in the marine environment as well as to humans.

Coral is also very sensitive, and a slight change in the conditions of the water in which it is living can drastically impact the coral. Coral bleaching, which more often than not leads to death of the coral, can be induced by changes in the water such as temperature, salinity, or pH.

Bleached coral showing the impact of sunscreen versus healthy coral.
Bleached coral showing the impact of sunscreen versus healthy coral.

Bleaching occurs when coral’s symbiotic algae, zooxanthellae, is expelled. Zooxanthellae is a photosynthetic algal species that lives on the coral, providing it with food and giving it its color. When something goes wrong and causes stress to the coral, the coral’s response is to expel the zooxanthellae in an attempt to regain its health. When this occurs, the coral loses its pigment and it turns white, hence the name coral bleaching. After a coral bleaches, it generally will not return to good health because of the loss of its energy source, the zooxanthellae.

Dr. Roberto Danovaro, a researcher in the Department of Marine Science at Polytechnic University of the Marche, Ancona, Italy, recently discovered that sunscreen has this impact on coral, causing bleaching and eventually death because of the effect of the chemicals that sunscreen contains. UV filters, a component in sunscreens and other cosmetics used on the skin, can contribute to coral bleaching. These compounds promote viral infections in the zooxanthellae, causing the coral to expel its symbiotic algae. After the algae is expelled, the coral will bleach and eventually die.

In recent years, people have become increasingly obsessed with skincare items like sunscreen and cosmetics in an attempt to prevent skin cancer along with other forms of skin disorders. Along with this increased interest, however, come detrimental effects on the environment, a neglected but important relationship that is worthy of consideration.

Although knowledge of thermal stress and rising ocean temperatures and their effects on coral is becoming more widely known, other sources of bleaching such as sunscreen are not as commonly understood. When people go for a swim at the beach, they’re not usually thinking about sunscreens or other cosmetics that might come off in the water, or how these products may impact the marine life around them. Yes, it’s nice to not get sunburned, but please be aware of what you’re putting on before you go in the water and the valuable marine life that may be affected.

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