The iridescent coral reefs that decorate our planet’s tropical shores are under threat. With near-constant attacks from all sides—from careless divers and overzealous fishers to invasive algae and pollution runoff—it’s no wonder the future of these habitats looks bleaker every year. This isn’t just a problem for beach dwellers and snorkeling aficionados. As author and oceanographer Sylvia Earle puts it, our “planet’s life support system is, in fact, the ocean,” and nowhere is this fact clearer than in the havens of biodiversity that comprise coral reefs.
Threats to Coral Reefs
These bright colors are put in jeopardy, however, when humans are brought onto the scene. Scientists estimate that human activity has already destroyed a fifth of Earth’s coral reefs, and half of those remaining face immediate or eventual destruction. That means fewer and fewer reefs adorn coastal seas every year. Myriad reasons illustrate why.
Ingredients in sunscreens slathered on by swimmers and snorkelers leach into the water, where they can lead deadly viruses to infect the zooxanthellae, the algae that live symbiotically inside coral polyps. Divers and boaters knock off chunks of coral or take pieces home as souvenirs. Sewage, agricultural runoff, and other pollutants likewise choke reefs. This ceaseless torrent of attacks hurts not only coral reef communities themselves, but also the human population depending on them for shoreline protection (“barrier reefs” slow waves approaching beaches, helping lessen coastal erosion), fish stocks, and tourism.
Perhaps the greatest threat to coral communities is global climate change. “The acidification, or increasing pH, of the ocean… caused by increased concentrations of carbon dioxide in the atmosphere” gravely imperils reefs, says oceanographer Jessica Amacher. Small changes in pH spell big trouble for corals because more acidic waters inhibit calcification, or the building of calcium-based reefs. And corals can only live within a limited temperature range; most already grow at the upper end of that spectrum.
According to the Nobel Prize-winning Intergovernmental Panel on Climate Change (IPCC), ocean heat content fluctuates from year to year, but a clear, gradual upward temperature trend exists. Raising seawater temperatures by just 1-2°C (about 2-4°F) can kill the reefs' algal symbionts or cause the polyps to expel them. Without these algae, corals lack the nutrients necessary to survive. Such reefs turn into bleached white ghost towns, devoid of the brilliant swarms of tropical fish that once flitted through the bustling coral metropolis.
Corals do have some built-in resistance to these stresses, but too much pressure can push damaged reefs to the brink of collapse. To recover, they need intervention from the very species that caused their problems in the first place: human beings. And the humans coming to the reefs’ rescue are trying out some rather peculiar techniques.
Building Artificial Reefs
In cases where corals are damaged beyond repair, researchers are building artificial reefs nearby to take their place. Researchers and state governments use sunken ships, planes and cars with engines removed, and even toilets in the southeastern U.S. as a framework for new reefs. Fish, crustaceans, and other reef inhabitants can use the structures for shelter, and new corals slowly begin to grow there. Old porcelain thrones, however, don’t exactly mimic the structure of a natural reef.
To address this problem, in 1993 scuba enthusiast Todd Barber started the Reef Ball Foundation, which builds and deploys specially designed concrete spheres to create new reefs. Marine biologist and professional diver Alissa Rickborn describes them as looking “like a ball of Swiss cheese, [and] they provide a substrate for things to grow on.”
Despite their bizarre appearance, the popularity of reef balls continues to grow; the non-profit has dropped more than half a million of them overboard in almost 60 countries, and the foundation is planning further projects in a dozen other nations. “In French Polynesia,” says Rickborn, researchers “have created a reef miles and miles long” with the concrete spheres. But Reef Balls and other artificial reefs still require existing corals to seed them, so they are only effective in regions near healthy reefs.
The enormous pressures humans exert on coral reefs may cause the idea of reef restoration to seem like a Herculean task. Not all threats can be directly addressed; those related to global climate change will require action from people and governments far removed from the coasts where coral reefs are slowly dying. But human ingenuity and dedication to preserving these fantastic environments, whether by creating new reef environments or battling to save imperiled existing ones, gives hope for corals’ survival in a changing ocean.
Amy Hansen - Amy Hansen is a biologist-turned-writer currently living in the San Francisco Bay Area. Though science writing is her true passion, she'll ...
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