Sunscreen can damage coral and reduce the temperature at which they “bleach” or turn white from heat stress. Stressed coral are more vulnerable to invasive algae, which then limit the ability of coral to recover. All the white coral in this photo became bleached in the last month. JEFF BAGSHAW / DLNR photo

Maui’s coral reefs are in trouble. Many of the hazards are complex and global — climate change and ocean acidification, for example — but there is a simple step we can take to protect coral: read the label on our sunscreen. Every day Maui residents and visitors leave an estimated 55 gallons of sunscreen in the water around the island.

Though oceangoing residents and visitors may be doing the right thing by protecting their skin, many of the sunscreens used contain reef-damaging compounds.

“If someone showed up and dumped a barrel of chemicals into the ocean, you’d call the EPA,” says Jeff Bagshaw of the state Department of Land and Natural Resources.

Bagshaw oversees public outreach and education for the Ahihi Kinau Natural Area Reserve on Maui. He and his team of volunteers are reaching out to the community about the impacts of sunscreen on the reef.

Corals suffer in two ways: First, the active ingredient in many sunscreens, oxybenzone, affects the DNA function in coral cells; mature corals end up sterile while coral larvae are deformed and unable to attach to rocks and form more reef. Second, oxybenzone causes juvenile corals to encase themselves in their own skeleton, where they starve.

Chemicals in sunscreen also increase the rate of coral bleaching. Normally, coral bleaching occurs when seawater reaches temperatures of 87-88 degrees. Corals then expel their zooxanthellae, symbiotic invertebrates that give corals both color and food through photosynthesis.

Oxybenzones, avobenzones and similar chemicals protect us from UV rays by absorbing light. When these chemicals end up on the reef, they continue to absorb light and “heat up” corals, essentially lowering the coral bleaching temperature by 9 degrees to 78-79.

In Ahihi Bay, these chemicals have been found at 14 times the “safe” level for coral to survive.

Elsewhere in Hawaii, levels are 40 times greater than what coral can tolerate. Bagshaw estimates 30 percent of the corals in and around Ahihi experienced dramatic bleaching last summer.

Some of these coral heads are 500 years old. A healthy reef can recover from an episode of coral bleaching, but many of the reefs around Maui are already weakened by invasive algae. As reefs bleach, these invaders move in, capitalize on blighted corals and smother their healthy neighbors. Over time, the skeletons of the reef break down to rubble. Coral reefs are critical to a healthy and functioning ocean ecosystem.

Like the ohia in the rainforest, corals are keystone species, essential to the function of the ecosystem. Corals provide habitat for fish and support marine food webs. “If we lose coral we lose fishing, surfing, even the structure of our shoreline,” says Bagshaw. Protecting your skin from sunburn is important — just use alternatives to chemical-based sunscreens.

Widely available mineral-based sunscreens are safe for the reef. Look for sunscreens with the active ingredients of zinc oxide or titanium dioxide and use those formulated for use in water. Rash guards and wet suits are a great form of sun protection and minimize worries about “gaps” when applying sunscreen to hard-to-reach places.

Read labels closely. “Reef-safe” doesn’t necessarily mean safe for coral as there are no official guidelines for labeling a product as reef-safe. Sunscreen is only one of 3,500 products that contain oxybenzone and oxybenzonelike chemicals.

Can’t remember the name? Heed this simple advice: “If you can’t say it, don’t spray it,” says Bagshaw.  For more information on sunscreens and reefs, stop by the Ahihi Kinau Natural Area Reserve or check out posts on the reserve’s Facebook page: Friends of Ahihi Kinau. You can also help educate others about reefs and ocean life. Contact Bagshaw at 264-7891 to join the reserve’s team of educational volunteers.

* Lissa Fox Strohecker is the public relations and education specialist for the Maui Invasive Species Committee. She holds a biological sciences degree from Montana State University. “Kia’i Moku,” “Guarding the Island,” is prepared by the Maui Invasive Species Committee to provide information on protecting the island from invasive plants and animals that can threaten the island’s environment, economy and quality of life.