Coral reefs, the “rainforests of the sea,”

coral reefs are some of the most biodiverse and productive ecosystems on earth. They occupy less than one percent of the ocean floor, yet are home to more than a quarter of all marine species: crustaceans, reptiles, seaweeds, bacteria, fungi, and over 4000 species of fish make their home in coral reefs. With a global economic value of $375 billion a year, coral reefs provide food and resources for more than 500 million people in over 100 countries and territories. But tragically, coral reefs are in crisis.

Coral reefs are endangered by a variety of factors, including: natural phenomena such as hurricanes, El Niño, and diseases; local threats such as overfishing, destructive fishing techniques, coastal development, pollution, and careless tourism; and the global effects of climate change—warming seas and increasing levels of CO2 in the water. According to Reefs at Risk Revisited, a report by the World Resources Institute, 75 percent of the world’s coral reefs are at risk from local and global stresses. About a quarter of them have already been damaged beyond repair. If we continue with business as usual, 90 percent of coral reefs will be in danger by 2030, and nearly all of them by 2050.

They provide natural buffers for coastal communities, preventing waves from destroying shorelines. The many types of fish swimming throughout their lattices, meanwhile, offer a ready supply of food for people.

What is coral?

Coral reefs are colonies of individual animals called polyps, which are related to sea anemones. The polyps, which have tentacles to feed on plankton at night, play host to zooxanthellae, symbiotic algae that live within their tissues and give the coral its color. The coral provides CO2 and waste products that the algae need for photosynthesis. In turn, the algae nourish the coral with oxygen and the organic products of photosynthesis. The coral uses these compounds to synthesize calcium carbonate (limestone) with which it constructs its skeleton—the coral reef.

The symbiotic relationship between corals and zooxanthellae can only exist within the narrow band of environmental conditions found in tropical and subtropical waters. The water must be clear and shallow so that the light algae need for photosynthesis can penetrate, and water temperatures must ideally remain between 23˚ and 29˚ C (77˚ to 84˚ F).

The number of coral species in each reef varies: the Great Barrier Reef off Australia has over 600 species of coral while a Caribbean reef has about 65. Today many reefs have 40 to 50 percent less coral than they did just 30 years ago.

A recent study of 159 reefs in the Pacific found that plastic pollution is killing coral, too. When coral reefs come into contact with plastic waste, the incidence of disease rises 20-fold. The scientists do not know exactly how the plastic causes disease, but they speculate that bacteria on the plastic can infect the coral and plastic can block the needed sunlight. By 2025, they project that 15.7 billion plastic pieces could come into contact with coral reefs.

In normal conditions, around 4% of corals suffer from disease. When corals encounter plastic pollution, that rate jumps to 89%.

The reason for the staggering increase isn’t precisely understood, the Atlantic reports, but the team of researchers have a few theories.

For instance, plastic can end up covering a coral, blocking the sunlight, and allowing diseases that thrive in shaded places to take root.

Or sharp pieces of plastic can stab a coral, creating a wound for bacteria to infect. Plastic can also act as a raft for pathogens to travel on, making it more likely for them to come into contact with corals.

Further, plastic pollution can work in conjunction with other afflictions that affect corals to weaken the overall resilience of reefs. For example, rising ocean temperatures are causing corals to bleach, which is when they expel the symbiotic organisms that live on them and give them color. The prevalence of plastic waste can make it harder for corals to rebound from this sickly fate once temperatures cool.

The range of ways that plastic can harm corals is broad, but the overall effects are clear — plastic pollution is causing a widespread decline, the Atlantic reported.

The team studied 124,000 corals over a four-year period and plastic pollution was most severe in Indonesia, Myanmar, and Thailand. The problem was less pronounced in Australia.

Globally, around 380 million metric tons of plastic are being created annually. Meanwhile, an estimated 8 million metric tons of plastic enter the oceans each year, which is like emptying a garbage truck of plastic into an ocean every minute.

Natural phenomena that stress coral reefs include predators such as parrotfish, barnacles, crabs and crown-of-thorns starfish, and diseases. Hurricanes or prolonged cold and rainy weather can harm coral reefs. The El Niño weather pattern, which can result in lower sea level, altered salinity due to too much rainfall, and elevated sea-surface temperatures, can also damage coral (oceans absorb 93 percent of climate change heat). When corals overheat, they react to the stress by expelling their algae, which results in coral bleaching.

An uncertain future

According to the IPCC’s Global Warming of 1.5˚ C report, if ocean temperatures rise 1.5˚ C, coral reefs are projected to decline 70 to 90 percent more; at 2˚C, we would largely destroy all our coral reefs.

Coral reefs provide us with food, construction materials (limestone) and new medicines—more than half of new cancer drug research is focused on marine organisms. Reefs offer shoreline protection and maintain water quality. And they are a draw for tourists, sometimes providing up to 80 percent of a country’s total income. Losing the coral reefs would have profound social and economic impacts on many countries, especially small island nations like Haiti, Fiji, Indonesia, and the Philippines that depend on coral reefs for their livelihoods.

The famous great barrier reef

The Great Barrier Reef is the largest and richest coral reef in the world because it has been protected since the early 1970s. After the creation of a marine sanctuary for Apo Island in the Philippines in 1982, the fish population tripled. Reefs at Risk Revisited also recommended curbing unsustainable fishing, managing coastal development better, and reducing both land and marine-based pollution. It also stressed the importance of comprehensive ecosystem management that includes all stakeholders, and the need to educate the public about the importance of coral reefs and investing in scientific research.

Some scientists are studying types of coral that can adapt to warmer ocean temperatures and survive bleaching, and using that information to “train” corals to adjust to warmer acidic water. Their goal is to eventually transplant these more resilient corals into the reefs.

The Coral Restoration Foundation protects and restores coral reefs through creating coral nurseries and transplanting corals into reef restoration sites. Concerned individuals can become citizen scientists and monitor corals at restoration sites, or volunteer to monitor marine sanctuaries, protect marine wildlife or clear ocean debris. Everyone can help coral reefs by practicing sustainable fishing, and eating only sustainably caught fish. When vacationing near coral reefs, be careful not to touch them and don’t buy souvenirs of coral or other marine species.

And it is crucial, of course, for national and international bodies, and for all of us to address the threats of climate change by curbing carbon emissions.

Students in Columbia’s Earth Institute Center for Environmental Sustainability (EICES) who want to learn more about coral reefs can take EICES’ spring break Coral Reef Ecology course in Bermuda in March 2018. It deals with the biology of corals, reef biodiversity, factors that impact coral reefs, and coral reef conservation and preservation.

Five endangered coral reefs:

  1. Seychelles Coral Reefs
  2. Kingman Reef in Hawaii
  3. Great Barrier Reef
  4. Caribbean Coral Reefs
  5. Southeast Asian Coral Reefs

seychelles coral reefs:

The archipelago nation of Seychelles lost up to 90% of its coral reefs after a catastrophic bleaching event in 1998. In 2016, another massive bleaching event struck and reversed the recoveries that had been made in the intervening years.

Now, the Seychelles government is in a race against time as it tries to protect its lucrative, beautiful, and ecologically essential reefs from being eliminated entirely, according to ABC News.

Within one reef, for instance, local conservationists have recovered, nurtured, and transplanted 50,000 coral fragments to promote a longer-lasting recovery, according to ABC.

kingman reefs in hawaii:

As ships travel the world, they carry species on their hulls. Sometimes, these species get deposited in foreign waters and cause mayhem by disrupting food chains and ecosystems.

Known as invasive species, these creatures are a major threat to the world’s coral reefs.

In Hawaii, the Kingman Reef is suffering from invasive algae species that are blotting out various forms of life and turning corals a dark green or black.

great barrier reefs:

Visible from space and stretching 1,400 miles in length, the Great Barrier Reef is one of the world’s most splendid natural wonders.

But for all its grandeur, these reefs are just as threatened as coral found elsewhere. In 2016, bleaching affected 90% of corals throughout Australia’s waters.

The Great Barrier Reef is also being damaged by coral-eating starfish, which have been responsible for half of the reef’s decline between 1985-2012.

caribbean coral reefs:

Although coral reefs are a main draw for tourism in the first place, tourism is one of the main drivers of the decline of coral reefs throughout the Caribbean.

As cruise ships travel throughout the Caribbean, ferrying tourists from island to island, massive amounts of waste are being poured into the water, polluting reef habitats and causing them to die.

Southeast Asian Coral Reefs:

There could be more pieces of plastic in the world’s oceans than fish by 2050. Nowhere is this frightening prospect more apparent than throughout the coral reefs of Southeast Asia, according to the World Resources Institute, where a potent mix of plastic pollution and overfishing are changing reef dynamics throughout the waters of various countries.

Now what can we do to protect these reefs?

Choose sustainable seafood.

  1. Learn how to make smart seafood choices at
  2. Conserve Water. The less water you use, the less runoff and wastewater that eventually find their ways back into the ocean.
  3. Volunteer. Volunteer in local beach or reef cleanups. If you don’t live near the coast, get involved in protecting your watershed.
  4. Corals are already a gift. Don’t give them as presents. It takes corals decades or longer to create reef structures, so leave them on the reef.
  5. Long-lasting light bulbs are a bright idea. Energy efficient light bulbs reduce greenhouse gas emissions. Climate change is one of the leading threats to coral reef survival.
  6. If you dive, don’t touch. Coral reefs are alive. Stirred-up sediment can smother corals.
  7. Check sunscreen active ingredients. Seek shade between 10 am & 2 pm, use Ultraviolet Protection Factor (UPF) sunwear, and choose sunscreens with chemicals that don’t harm marine life. For more information, visit
  8. Be a marine crusader. In addition to picking up your own trash, carry away the trash that others have left behind.
  9. Don’t send chemicals into our waterways. Nutrients from excess fertilizer increases algae growth that blocks sunlight to corals.
  10. Practice safe boating. Anchor in sandy areas away from coral and sea grasses so that the anchor and chain do not drag on nearby corals.