Can Coral Reefs Survive Global Warming?

In just the last year, the scientific community produced a plethora of studies that have quashed any lingering doubt – global warming is here, and it is damaging the ocean.

This just confirms what many divers have seen with their own eyes. Bleached-out corals used to be a rarity. Now the ghostly white skeletons of dead or dying corals are a common sight in the Florida Keys, throughout the Bahamas and the Caribbean, around Pacific Island and even in the most remote Pacific coral atolls. Last summer, hot water caused the worst coral bleaching ever observed in reefs from Florida to Panama.

Long strands of dull, gray-green algae and seaweeds now dominate reefs once alive with colorful corals and other organisms that build the structures that have supported reefs for thousands of years. Corals and the many other reef species that make shells to protect themselves have evolved and persisted in a mildly alkaline ocean for billions of years; now they are rapidly dissolving in a sea that is becoming an acid bath. The impact of global warming on coral reefs boggles the mind—the fact that our pollution could be changing the temperature and chemistry of the vast and powerful ocean is nearly incomprehensible. But it’s true.

The complex linkages between the pollutants that spew out of our SUVs, factories, jet planes and dive boats, and the delicate corals surrounded by the fascinating fish, octopi, and eagle rays we travel far to see are becoming clearer. Every year, each American is responsible for about 15,000 pounds of carbon equivalents, a measure of global warming pollution that combines the effects of carbon dioxide (from burning fossil fuels), methane (from animal husbandry and landfills), nitrous oxide (from agriculture) and other gases. About 16 percent, or 2,300 pounds, of those emissions comes from driving ourselves around in a ton of steel, glass, and rubber. The rest comes from heating and cooling our homes, powering our appliances, growing the food we eat, manufacturing the goods we use, and enjoying other fruits of the American lifestyle.

These pollutants rise into the atmosphere, where they trap heat that warms the earth. There have already been many impacts of global warming on land. The harlequin frog and the golden toad of Costa Rica have apparently gone extinct as a direct result of warming. Glaciers are melting at record rates, disrupting normal patterns of river flow and damaging species that depend on these rivers. Rising sea levels are ruining freshwater supplies in small island nations like Tuvalu and the Solomon Islands, making them more vulnerable to storms and flooding.

But the first whole ecosystems to fall victim to global warming have been coral reefs.

Most corals are already close to their maximum temperature tolerance. Just a couple of degrees of warming can put them over the top, resulting in the loss of “zooxanthellae,” their symbiotic partners that turn sunlight into food for the corals. Corals that lose these partners slowly starve, and thus have far less capacity to reproduce and keep up with the erosion of their limestone skeletons. Many eventually die.

Corals have kept up with natural increases in sea level over the millennia, but now sea level is rising so fast that it threatens to drown many reefs—when the water gets too deep, the zooxanthellae can’t photosynthesize anymore. Logging mangrove forests for charcoal and to make room for shrimp farms removes the buffer between coral reefs and the land. As a result, more silt and pollution enter the water, harming not only the reefs but also the sea grass meadows that often surround patch reefs. These meadows are extremely sensitive to silt and pollution and they need lots of light to thrive, but pollution allows algae to overgrow and kill seagrass. Many coral reef species like conch, turtles, and French grunts depend on the meadows for food and the reefs for shelter in the reef, where their waste products are used by corals to grow. Less seagrass means less nutrition for corals.

On top of all that, we’ve made coral reefs more vulnerable by recklessly blowing them up to harvest fish, using cyanide to capture live fish for the aquarium trade, dumping sewage into them, and allowing pollution from farms and poorly managed land to run right into ocean waters. Coral reefs depend on very clean, very clear water to survive. Silt and pollution stress them out, sometimes causing bleaching and often causing slower growth, disease and overgrowth by aggressive seaweeds that take over the reef. Killing excessive numbers of coral reef fish, many of which eat the seaweeds, makes matters worse.

When you are sick and stressed out, the first step toward better health is to remove as many stresses from your life as possible. You stay home, rest, and eat healthy food to help your body fend off the illness, right? That’s the best prescription for coral reefs, too. We need to reduce their overall stress level by stopping destructive fishing practices, sewage pollution and polluted runoff.

Of course, when you are really sick, it’s important to take your medicine to attack the cause of the illness, even if it tastes bad or is painful in the short term. In the case of global warming, the medicine includes strong state and federal laws that cap emissions of the pollutants from utilities, industry, agriculture, cars and trucks that cause global warming. Furthermore, we must encourage ways to suck these pollutants out of the atmosphere, such as by planting trees and changing the way we farm crops. While some things we must do to fight global warming will impose costs on all of us, many make sense in their ownright by saving money and contributing growth to the economy. In the U.S., one of the most profligate energy users in the world, there is a huge margin for increased energy efficiency without harming economic productivity.

Divers can help by volunteering to monitor coral reefs (with organizations like ReefCheck, for example) and by educating others who are not as intimate with reefs as we are. We can support the organizations working hard to fight serious threats to reefs and respond to their action alerts with emails, phone calls and letters to the policymakers who can make a difference. Some of these organizations are listed below.

Coral reefs need all the help they can get to cope with the inevitable warming, acidification and sea-level rise that is happening now and will continue over the next few decades. And they also need us to drive more fuel-efficient cars, buy more energy-efficient appliances, and turn down the thermostat in the winter and the AC in the summer. Governments need to respond to global warming, but each company and consumer has a moral responsibility to respond as well. Global warming is already affecting our planet and poses a grave threat to our well-being and that of our co-inhabitants on Spaceship Earth. Each of us must rise to this generational challenge with ingenuity, commitment and compassion.

Author Rod Fujita, Ph.D., is a marine ecologist with Environmental Defense and a member of the Board of Directors of the Coral Reef Alliance. He is the author of Heal the Ocean: Solutions for Saving Our Seas, which is available at www.undercurrent.org. All our books’ profits go to saving coral reefs.