Coral reefs are one of the most diverse and important ecosystems on the planet. They provide a habitat for marine life from pelagics to reef fish. They also protect coastlines from storms/ erosion and support local economies through tourism and fishing.
These vital ecosystems are under a huge threat from lots of things, including rising sea temperatures, ocean acidification, pollution, and overfishing. One of the most significant threats facing reefs today is coral bleaching. This is where coral colonies expel algae that live inside them, and they turn white and probably die from diseases.
Coral bleaching has been occurring naturally for millions of years but recently it has become more common and severe. According to the National Oceanic and Atmospheric Administration (NOAA), there have been three global coral bleaching events since 1998. All of these have affected hundreds of millions of coral colonies around the world.
In this article, we will examine the statistics surrounding coral bleaching, including its causes, impacts, and trends over time.
Causes of Coral Bleaching
Coral bleaching occurs when the symbiotic relationship between coral and the algae that live inside them break down. The relationship is essential for the survival of coral colonies. Algae provide the coral with most of its food through photosynthesis.
When water temperatures rise above a certain threshold, the algae begin to produce toxic substances. In response to the toxins, the coral expels the algae, leaving behind the white calcium carbonate which is the skeleton of the coral.
Other factors can also contribute, including pollution, overfishing, and ocean acidification. Pollution from agricultural runoff, sewage, and other sources can increase the number of harmful nutrients in the water. This leads to algal blooms that block out sunlight suffocating the coral colonies.
Overfishing can disrupt the balance of the coral ecosystem, leading to an increase in algae and other organisms that can hurt and kill the coral.
Ocean acidification is caused by the absorption of carbon dioxide into the ocean. This can make it harder for coral to build and maintain their skeletons.
Impacts of Coral Bleaching
Coral bleaching has a range of impacts on the ecosystems, creatures, and communities of people that rely on it for their livelihoods.
When corals die, they leave behind barren skeletons that provide little to no habitats or protection for marine life. This can lead to a plethora of ecological impacts, as creatures rely on coral for shelter/ food and need to find new homes or die.
The loss of coral reefs can lead to increased coastal erosion and storm damage as well. The reefs help to protect shorelines from the effects of waves/ storms.
The economic impacts of coral bleaching can also be significant and a lot of areas rely on coral reefs for tourism and fishing. According to the World Resources Institute, the global economic value of coral reefs is estimated to be between $375 billion and $475 billion per year.
Coral Bleaching Facts and Statistics
Coral bleaching is complex and a multifaceted phenomenon. Its impacts can vary widely depending on location, the severity of the bleaching, and the resilience of the coral species.
Coral bleaching happens when coral loses its vibrant coloration due to stress, resulting in the death of the coral.
The leading cause of coral bleaching is climate change, which raises ocean temperatures and makes the water more acidic.
The first recorded instance of coral bleaching was in the 1980s.
The first major global bleaching event occurred in 1998, affecting the reefs in the Indian and Pacific Oceans.
The frequency and severity of coral bleaching events have increased since 1980.
The most severe event on record occurred between 2014 and 2017.
More than 70% of the world’s coral reefs were affected by the 2014-2017 global bleaching event.
The 2014-2017 bleaching lasted longer than previous global bleaching events, with some reefs experiencing bleaching for over 12 months.
The Great Barrier Reef has been severely affected by coral bleaching events in recent years.
In 2016, 93% of the Great Barrier Reef was affected by bleaching.
The Caribbean has also been severely affected in recent years.
Coral reefs provide habitats for more than 25% of marine life, making them one of the most important ecosystems on the planet.
Coral reefs are also an important source of food and income for people around the world.
The economic value of coral reefs is estimated to be around $375 billion per year.
Coral bleaching has an indirect impact on the wider ecosystem, such as making coral more susceptible to disease and predation.
The loss of coral reefs can result in the loss of coastal protection from storms and hurricanes.
Coral bleaching events are more frequent in the Caribbean since the 1970s.
The frequency of coral bleaching events in the Caribbean is expected to increase.
The Pacific Ocean is home to the largest and most diverse coral reefs in the world.
Coral reefs in the western Pacific Ocean are particularly vulnerable.
Some species of corals are more resilient to bleaching than others.
Coral reefs in areas with lower levels of human impact are more likely to recover.
Areas with higher levels of human impacts, like pollution and overfishing, are less likely to recover.
The loss of coral reefs results in a loss of biodiversity.
Coral reefs are home to over 4,000 species of fish.
The loss of coral reefs results in the loss of cultural heritage to indigenous communities.
Coral reefs can serve as natural laboratories for research.
The loss of coral reefs can result in the loss of new medicines as they are an untapped resource.
Coral reefs are found in over 100 countries in the world.
Special corals can live for more than 400 years.
Coral reefs can grow at a rate of up to 7.9 inches (20cm) a year.
Coral reefs can protect shorelines from erosion and storm surges.
The ocean absorbs more than 90% of the heat from climate change.
The ocean has absorbed more than 25% of the carbon dioxide from human activity.
The ocean is becoming more acidic as it absorbs more carbon dioxide from humans.
Acidification of the ocean can make it harder for coral to grow and form.
Coral reefs are more vulnerable to bleaching during El Niño.
El Niño has happened more frequently due to climate change.
Coral bleaching is not limited to tropical areas.
Even the Mediterranean Sea has experienced coral bleaching in recent years.
In extreme conditions, Coral bleaching can happen in as little as two weeks.
Coral reefs in the Red Sea are more resilient to bleaching due to their high salt levels.
The loss of coral reefs affects snorkeling and scuba diving.
Coral bleaching impacts tourism, which has economic impacts on local communities.
Coral reefs provide inspiration for artists and photographers.
Some coral species can fluoresce under ultraviolet light.
Coral reefs can also provide inspiration for biomimicry, where engineers and scientists look to nature for solutions to engineering challenges.
Some major threats are overfishing, pollution, and physical damage from boats and anchors.
Efforts to mitigate coral bleaching include reducing greenhouse gas emissions/ pollution and creating marine protected areas to limit human impacts.
The Global Coral Bleaching consortium says that coral reefs represent 0.1% of the ocean floor, but support approximately 25% of marine species.
- NOAA Coral Reef Conservation Program. “What is Coral Bleaching?” https://coralreef.noaa.gov/education/beyond-bleaching/what-is-coral-bleaching/
- National Geographic. “Coral Bleaching.” https://www.nationalgeographic.com/environment/2019/01/coral-bleaching/
- National Oceanic and Atmospheric Administration. “Global Coral Bleaching Event: Status and Informational Resources.” https://www.noaa.gov/education/resource-collections/ocean-coasts-education-resources/global-coral-bleaching-event
- The Guardian. “Great Barrier Reef: 93% of corals hit by coral bleaching.” https://www.theguardian.com/environment/2016/apr/19/great-barrier-reef-93-of-corals-hit-by-coral-bleaching
- Coral Reef Alliance. “The Economic Value of Coral Reefs.” https://coral.org/coral-reefs-101/c