With the summer season fast approaching, there has been a resurgence of concern over water-enthusiasts’ sunscreens potentially harming fragile coral reef systems.

The need for sun protection is undeniable but as swimmers, divers and general ocean-lovers, how do we ensure that the products we out on our body are not harming corals?

In this article, I’m going to present you with all the facts and evidence linking coral bleaching and degraded reefs to swimmers’ sunscreen and determine the legitimacy of these claims.

The Claim

Four common sunscreen components can activate dormant viruses in coral’s symbiotic algae, known as zooxanthellae, that live within the reef’s tissues. The UV filters implicated are butylparaben, ethylhexylmethoxycinnamate, benzophenone-3 and 4-methylbenzylidene camphor. These ingredients, commonly found in many chemical sunscreens, are touted to cause complete coral bleaching at very low concentrations.

These sunblock chemicals stimulate viral replication until coral’s zooxanthallae explore, releasing viruses into the surrounding seawater, where they can infect neighboring coral reef systems. Claims have been made that about 4,000 to 6,000 metric tons of sunblock from swimmers wash-off into the world’s oceans annually, and that up to 10% of coral reefs are threatened by sunscreen-induced bleaching.

The Evidence

The study by an Italian team of scientists, R. Danovaro, L. Bongiorni, C. Corinaldesi, et al., published in Environmental Health Perspectives is the one piece of research done in support of sunscreen chemicals killing zooxanthallae and subsequently causing coral bleaching.

The Set-up

Coral branches of Acropora spp. and others were taken from tropical reefs in the Atlantic, Indian, and Pacific Oceans, as well as the Red Sea.

In situ and laboratory experiments were conducted by adding sunscreen aliquots and common UV filters to the corals. Using epifluorescence and microscopy, the zooxanthellae were monitored for viral infection and transmission.

The Findings

The Italian group of scientists found that the sunscreen ingredients killed coral and zooxnathallae withing 4 days by stimulating viruses (a 15-fold increase was observed in infection).

Experiments applying various sunscreen SPFs and concentrations to several coral species from different sites all proved to bleach corals.

The researchers concluded that based on a theoretical estimate of number of tourists using sunscreens in reef areas that up to 10% of the world’s coral reefs could be at risk for bleaching via sunscreen wash-off.

Also of note, R. Danovara et. al found that the coral bleaching effect was not dose-dependent, so reefs exposed even to very small concentrations of sunscreen are at risk.

The Verdict

Previous research has indicated that sunscreens can potentially bioaccumulate in the food chain and there may be a breakdown of sunscreens into toxic substances, until this most recent study, a link has never been shown between swimmers’ sunblock and coral reef bleaching (Leon-Gonzalez, 2011; Morohoshia, 2005).

Currently, there has only been one study published linking sunblock chemicals to the death of coral reefs published by R. Danovara, et al. And while published in a peer-reviewed journal, meaning the article has been critically assessed by a panel of scholars in the author’s, more studies will be needed to effectively conclude that swimmer’s sunscreens are putting 10% of the world’s coral reefs at risk of bleaching.

A completely in laboratory experiment cannot possible conclude that 10% of the world’s reef systems (outside of the experiment’s specific lab conditions) are at risk for bleaching from swimmers’ sunscreens.

I have no doubt under the exact laboratory conditions utilized in this study that corals will bleach. Corals are highly sensitive organisms and prone to bleaching at the slightest stress (sensitivity varies by species of course).

First, fracturing corals into nubbins and transporting them out of their ocean environment is always a risky business. It is very difficult to maintain corals (especially less hardy species such as Acropora) in lab conditions. The coral pieces used in experiments may have bleached with the addition of sunscreen aliquots because they were already highly stressed from the transport or due to other factors of the lab set-up (improper water temperature, poor water circulation, etc.). This may not be the case, but it was not discussed in the paper.

Second, the experimental set-up of immersing hands covered with sunscreen agents in a small water volume containing the coral pieces subjects the corals to a much higher concentration of sunscreen than they may experience out in the open ocean.

R. Danovara does indicate that even at low toxicity levels of sunscreen agents, corals may bleach. However, I’d like to see the results replicated a number of times and then more testing done in the ocean to confirm that sunscreen wash-off and the amount it is diluted in the sea actually causes reef bleaching.

A coral expert at the Florida Institute of Technology (FIT), Robert van Woesik, also questions whether the conditions utilized in the study truly reflect those found in nature.

This study certainly does have large implications for marine scientists running lab experiments with corals or managers of coral nurseries, as clearly a chemical sunscreen could cause bleaching and mortality of your coral specimens during testing in small water volumes.

However, until more research comes out, I’m still a firm believer that other human-induced pressures, such as pollution, sedimentation, overfishing and global warming, are much larger contributors to reef degradation than swimmers’ sunscreens.

Eco-Friendly Sunscreens

Even though I’m not in full agreement with the study discussed above, I do agree that ingredients in chemical sunscreens may be bad for human health as well as have the potential to bioaccumulate in the food chain.

If you’re looking for “reef safe” greener sunscreens, as I have been, I’ve got you covered! Whether you believe in the potential impact of chemical sunblocks on corals, you can reduce any risk to reef and ocean systems by choosing only sunscreens with physical UV filters (ie. titanium dioxide and zinc oxide). There are also a couple eco-friendly chemical sunscreens, just be sure to avoid sunblocks with octylmethoxycinnamate, benzophenone-3, parabens or octocrylene.

Here are my sunscreen recommendations:

  • Badger produces some great natural, water-resistant sunscreens and is rated highest for safety and efficacy by the Environmental Working Group.
  • Caribbean Solutions has another reef-safe, natural sunblock.
  • Loving Naturals produces a zinc-based sunscreen with 100% natural ingredients.
  • Reef Safe (made by Tropical Seas) claims to be completely for marine life.
  • And of course, staying in the shade and wearing hats and cover-ups are also great ways to protect yourself from the sun

What do you think of this article? Post your comments and questions below and I’ll answer. I’d love to know whether after reading this post, you’re going to switch to a “reef safe” sunscreen and why!

To The Ocean,

Christine

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