One common chemical in sunscreen can have devastating effects on coral reefs. Now, scientists know why.
Sea anemones, which are closely related to corals, and mushroom coral can turn oxybenzone — a chemical that protects people against ultraviolet light — into a deadly toxin that’s activated by light. The good news is that algae living alongside the creatures can soak up the toxin and blunt its damage, researchers report in the May 6 Science.
But that also means that bleached coral reefs lacking algae may be more vulnerable to death. Heat-stressed corals and anemones can eject helpful algae that provide oxygen and remove waste products, which turns reefs white. Such bleaching is becoming more common as a result of climate change (SN: 4/7/20)
The findings hint that sunscreen pollution and climate change combined could be a greater threat to coral reefs and other marine habitats than either would be separately, says Craig Downs. He is a forensic toxicologist with the nonprofit Environmental Laboratory in Amherst, Va., and was not involved with the study.
Previous work suggested that oxybenzone can kill young corals or prevent adult corals from recovering after tissue damage. As a result, some places, including Hawaii and Thailand, have banned oxybenzone-containing sunscreens.
In the new study, environmental chemist Djordje Vuckovic of Stanford University and colleagues found that glass anemones exposed to oxybenzone and UV light add sugars to the chemical. While such sugary add-ons would typically help organisms detoxify chemicals and clear them from the body, the oxybenzone-sugar compound instead becomes a toxin that’s activated by light
Anemones exposed to either simulated sunlight or oxybenzone alone survived the length of the experiment, or 21 days, the team showed. But all anemones exposed to fake sunlight while submersed in water containing the chemical died within 17 days
The anemones’ algal friends absorbed much of the oxybenzone and the toxin that the animals were exposed to in the lab. Anemones lacking algae died days sooner than anemones with algae.
In similar experiments, algae living inside mushroom coral also soaked up the toxin, a sign that algal relationships are a safeguard against its harmful effects. The coral’s algae seem to be particularly protective: Over eight days, no mushroom corals died after being exposed to oxybenzone and simulated sunlight.
It’s still unclear what amount of oxybenzone might be toxic to coral reefs in the wild. Another lingering question, Downs says, is whether other sunscreen components that are similar in structure to oxybenzone might have the same effects. Pinning that down could help researchers make better, reef-safe sunscreens.
Coral belongs to the class Anthozoa in the animal phylum Cnidaria, which includes sea anemones and jellyfish. Unlike sea anemones, corals secrete hard carbonate exoskeletons that support and protect the coral. Most reefs grow best in warm, shallow, clear, sunny and agitated water. Coral reefs first appeared 485 million years ago, at the dawn of the Early Ordovician, displacing the microbial and sponge reefs of the Cambrian
Sometimes called rainforests of the sea, shallow coral reefs form some of Earth's most diverse ecosystems. They occupy less than 0.1% of the world's ocean area, about half the area of France, yet they provide a home for at least 25% of all marine species, including fish, mollusks, worms, crustaceans, echinoderms, sponges, tunicates and other cnidarians.[8] Coral reefs flourish in ocean waters that provide few nutrients. They are most commonly found at shallow depths in tropical waters, but deep water and cold water coral reefs exist on smaller scales in other areas
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