Corals may lead a plant-like existence, but they are animals. Specifically, they are polyps that require outside sources of food and oxygen. They get much of both from algae called zooxanthellae, organisms that live on coral reefs and bestow upon the reefs their vivid colors. The algae also provide the polyps with the nutrients they need. In return, the polyps give the algae shelter.
Coral reefs are created when free-floating larvae settle on hard surfaces like rocks. Polyps secrete calcium carbonate underneath them, forming reefs in the process. Reef build-up happens slowly: it can take from one hundred thousand to thirty million years for a barrier reef to mature.
Related to jellyfish, many coral polyps are coin-sized or smaller. But as they grow and collect, they can form reefs weighing in the tons. The reefs are among the most diverse ecosystems on the planet. They give habitat to more than 25% of all known varieties of marine life including fish, sponges, clams, and crabs. They are important to nearby seagrass, mangrove, and mudflat communities.
Found in the waters of more than one hundred countries, over 500 million people base their livelihoods or are otherwise dependent upon the reefs. Coral reefs add about $375 billion annually to the worldwide economy, according to the National Oceanic and Atmospheric Administration (NOAA), a US government agency. Revenue based on tourism, coastal development, and commercial and recreational fishing heavily contribute to this economic value.
Coral reefs offer protection from angry ocean waters churned up by tropical storms, thereby mitigating erosion and flooding, and protecting against loss of life. Coral reefs are also a source of new medicines: chemical compounds produced from reef organisms are being developed to combat cancer, heart disease, and viruses. Many indigenous people tie their existence to the reefs. Aboriginal and Torres Strait Islanders base spiritual and cultural values on Australia’s Great Barrier Reef, using it responsibly and sustainably in the process.
Natural Phenomena and Human Activities Threaten Coral Reefs
Natural threats to coral reefs can come from powerful storms like hurricanes and cyclones. El Niño events can cause warmer water temperatures, rising sea levels, and higher salt content—all are threats to corals. Other threats come from disease and predatory activities from fish, crabs, and sea stars. Even plastic settling on reefs can have a negative impact.
But the greatest threat comes from rises in the temperature of ocean waters due to human activities. A water temperature increase of 1.5°C this century could result in losses of 70% to 90% of the world’s coral reefs. A temperature rise of 2°C could result in elimination of nearly all reefs.
When surface water temperatures rise above a preferred range, corals expel the algae living on them, thus turning the reef white. Known as coral bleaching, the polyps can starve and eventually die. The Great Barrier Reef bleaching event of 2016 killed 22% of the corals, according to the Australian Institute of Marine Science. The World Economic Forum says the reef has experienced five bleaching events since 1998.
Ocean acidification, another byproduct of human activity, also causes problems. About a fourth of atmospheric carbon dioxide (CO2) winds up in oceans, leaving the water more acidic. Elevated CO2 levels dissolve seashells and make it harder for marine animals to grow. That is bad news—too much CO2 can erode existing reefs and inhibit new growth.
Promising Efforts to Preserve and Restore Coral Reefs
Australian waters contain about 17% of the world’s coral reefs. The Great Barrier Reef accounts for about 10% of that; that is about 344,400 square kilometers (34.44 million hectares), which is approximately equivalent to the area of Japan. It is no wonder that Australia values such a spectacular structure and is actively restoring it.
"The Great Barrier Reef Marine Park Authority not only protects the reef but also promotes it’s sustainable use."
In 1975, Australia instituted the Great Barrier Reef Marine Park Act. Under this act, the Great Barrier Reef Marine Park Authority was created. The Park Authority not only protects the area but also promotes its sustainable use. Regulatory programs such as the 2004 expansion of take and no-take zones demarcated areas where activities such as fishing, mining, and drilling can occur. According to the Park Authority’s website, no-take zones were increased from less than 5% to 33%. Since then, the reef has experienced several benefits:
There are more fish in the area and their average size is increasing.
There are fewer and less severe predator outbreaks.
Disturbances from a single bleaching event, predators, and coral disease were down 30% in no-take zones, and they recovered 20% faster than nearby take zones.
Strategies to preserve coral reefs are being explored. Researchers at the University of Miami in the US found that one species—the mountainous star coral—can adapt to high temperatures and acidity. The mountainous star corals survived prolonged periods of heat and quickly recovered when temperatures returned to normal levels. Unfortunately, researchers found a downside: the reproductive ability of the species declined.
Australia’s Reef Restoration and Adaptation Program has begun a program to find new ways to help corals adapt to climate change. The plan is for successful techniques developed in the program to be shared around the world.
Researchers funded by the Australian Institute of Marine Science are studying other ways for corals to survive climate change, such as developing heat-resistant algae. Thus far, ten heat-tolerant strains have been developed. All showed an increased ability to withstand heat over wild algae.
A new technique led by Peter Harrison, a professor at Australia’s Southern Cross University, called the Coral IVF program, is showing signs of success. Many corals reproduce by spawning and spewing eggs and sperm into the water for fertilization. In the Coral IVF process, eggs and sperm are collected from healthy reefs and grown in pools. Once of sufficient size, they are transplanted to damaged reefs. The program resulted in transplanted corals growing successfully.
The Coral IVF technique brings another improvement to their restoration. When the polyps are grown together with mutually supporting algae, the polyps show greater heat tolerance.
Possibility of Successful Coral Restoration Projects Worldwide Provides Hope
The success of the Coral IVF program is cause for hope. Harrison began his first experiment in Singapore in 2015 and brought it to the Great Barrier Reef in 2016. The first corals to be spawned and planted on damaged reefs became mature enough to begin spawning in 2021. Harrison told Tony Moore, a reporter from The Sydney Morning Herald, that the Singapore reef-spawned corals have grown from microscopic to plate-sized and were reproducing in just three years.
With the success of the program demonstrated on two reef systems, Harrison said that carrying the process to a larger scale is possible. “All of this is doable,” he told Moore.
Whether caused by predatory damage, global warming, or natural disease, corals are suffering. If everyone reduces their carbon footprint even a little, the survival of corals seems much more likely.
*Cassie Journigan is a writer who lives in the north-central region of Florida in the United States. She focuses on issues related to sustainability. She is passionate about numerous topics including the Earth’s changing climate, pollution, social justice, and cross-cultural communications.