Summer is coming, and we’ll all start applying sunscreen to protect our skin from the sun’s radiation. With that, the conversation will start again about the effect of sunscreen on ocean creatures, because the human reach has spread out over the whole world. What we do on the surface, affects the creatures on the bottom of the ocean. Yet, we still need to discover what the influence of human behavior is on those creatures.  

Until recently, we knew that oxybenzone, a molecule in sunscreen, damages coral reefs, but we didn’t understand how. Scientists from Stanford University have discovered why oxybenzone is damaging coral reefs and provided the opportunity to research the damaging effects of other molecules.

When cells try to metabolize oxybenzone, they replace the hydrogen (highlighted in red on the left) with a sugar group (in red on the right). This turns the sunscreen into a toxin. Image credit Djordje Vuckovic, CC BY-ND

When you apply sunscreen, oxybenzone protects your skin from harmful UV radiation by absorbing light and transforming it to heat. If you go swimming afterward, the sunscreen will wash off into the water. The molecules present in the sunscreen will travel through the water and will eventually be absorbed by corals and sea anemones. When these sea creatures try to metabolize and break down the molecule, they replace a hydrogen atom with a sugar group. This is a common step in metabolism, in both coral, anemones, and humans alike, to make molecules easier to transport through the body. However, by adding a glucose group to the oxybenzone, instead of converting the energy from light to heat, it uses the energy to start a reaction that damages cells. So, instead of making it easier to metabolize, the molecule becomes toxic. 

Darker-colored anemones on top with algae lived longer than the lighter-colored anemones on the bottom that did not have symbiotic algae. Image credit Djordje Vuckovic and Christian Renicke, CC BY-ND

Symbiotic algae that live together with corals might come to the rescue. Scientists found that the algae take up some of the toxins produced by corals. However, because of the increasing temperatures and acidification of the ocean, the corals are bleaching and expelling the algae. They are losing protection from the harm of their self-produced toxin. 

Luckily for the corals, improved sunscreens are available that do not contain oxybenzone. However, scientists need to figure out if the replacing molecules are truly harmless for the corals and anemones and do not become toxic when metabolized. We need to discover our influence on the deepest oceans and highest mountains to prevent problems. 

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