The Coral Triangle (CT) is a triangular-shaped area in the tropical waters near Indonesia, Malaysia, Papua New Guinea, the Philippines, the Solomon Islands, and Timor-Leste. This region has at least 500 species of reef-building corals in each area. The Coral Triangle is located between the Pacific and Indian Oceans and includes parts of two biogeographic regions: the Indonesian-Philippines Region and the Far Southwestern Pacific Region. As one of eight major coral reef zones worldwide, the Coral Triangle is known as a global center of marine biodiversity and a top priority for conservation. Its rich biological resources make it a key area for marine life. Often called the "Amazon of the seas" (similar to the Amazon rainforest in South America), it covers 5.7 million square kilometers of ocean. It contains more than 76% of the world’s shallow-water reef-building coral species, 37% of its reef fish species, 50% of its razor clam species, six out of seven sea turtle species, and the world’s largest mangrove forest. The highest coral diversity is found in the Bird’s Head Seascape of Indonesian Papua, which has 574 species (95% of the Coral Triangle and 72% of the world’s total). In 2014, the Asian Development Bank reported that the marine ecosystem in the Coral Triangle is worth about $1.2 trillion each year and provides food for over 120 million people. According to the Coral Triangle Knowledge Network, the region earns about $3 billion annually from fish exports and another $3 billion from coastal tourism.

The World Wide Fund for Nature considers the Coral Triangle a top priority for marine conservation and works to protect the region through its Coral Triangle Program, started in 2007. One important area of biodiversity is the Verde Island Passage in the Philippines. The Tubbataha Reef Natural Park in the Philippines and the Raja Ampat UNESCO Global Geopark in Indonesia are coral reefs in the region that have been designated UNESCO World Heritage Sites.

Biodiversity

The Coral Triangle covers only 1.6% of the world’s ocean area, but it is home to 76% of all known coral species. It also supports 52% of Indo-Pacific reef fish and 37% of all reef fish globally, making it the most diverse area for coral reef fish. More than 3,000 species of bony fish live in the Coral Triangle, spread across over 90% of its region. Some of the largest fish found here include the whale shark, coelacanth, and chimaerans.

The Coral Triangle is the center of marine biodiversity, not only for corals and fish but also for many other ocean creatures. It is home to about 950 species of molluscs and 458 species of crustaceans. Six out of the world’s seven marine turtle species also live in this region.

Thirteen percent of the Coral Triangle has been identified as areas with high marine biodiversity. These include parts of the southern Philippines, northeastern Sabah in Malaysia, central to eastern Indonesia, eastern Papua New Guinea, and the Solomon Islands. The areas with the highest number of species make up only 6% of the Coral Triangle’s total area. These regions include parts of the Philippines (such as Luzon, Bohol, Mindanao, Palawan, and the Sulu Archipelago), Malaysia (northeastern Sabah), Indonesia (northern and southeastern Sulawesi, the Banda Sea, Maluku Islands, and Raja Ampat), Papua New Guinea (Madang Province, New Britain, Milne Bay, the Louisiade Archipelago, and Bougainville Island), and the Solomon Islands (Guadalcanal and Makira-Ulawa Province). However, more than half (70%) of the Coral Triangle’s areas have low species richness.

Important marine biodiversity sites in the Coral Triangle include the northern tip of Sulawesi, Ambon Island, the Kai Islands, the Raja Ampat Archipelago, the Verde Island Passage in the Philippines, the southern part of Negros in the Philippines, and Cebu in the Philippines.

The largest mangrove forests in the world are also found in the Coral Triangle. These forests support a wide range of habitats and environmental conditions, which help maintain the region’s high biodiversity.

The Coral Triangle includes between 10 and 19 seagrass species, which belong to four families (Hydrocharitaceae, Cymodoceaceae, Zosteraceae, and Ruppiaceae). These seagrass species cover nearly 58,550.63 square kilometers. A total of 21 seagrass species have been found in this region.

In 2008, an Indonesian–U.S. marine survey discovered deep-sea biodiversity and active underwater volcanoes at a depth of 3,800 meters along the western ridge. Scientists found about 40 new deep-sea coral species in this area. Most of these corals are white because the region lacks colorful algae, which typically live in shallower waters. Hydrothermal vents and coral reefs at 4,000 meters also support unique species, such as marine shrimps, crabs, barnacles, and sea cucumbers.

According to Indonesia’s Minister of Research and Technology, Bambang Permadi Soemantri Brodjonegoro, the Coral Triangle needs more taxonomists and oceanographers to study and protect its biodiversity. He stated that the goal of this research is to increase knowledge and use that knowledge to protect coastal and marine life from extinction.

Scientists have proposed three theories to explain why the Coral Triangle has such high species diversity. These are called the "center of origin" model, the "center of overlap" model, and the "center of accumulation" model.

• The center of origin model suggests that the high diversity in the Coral Triangle came from a central ancestral population that later spread to other areas.
• The center of overlap model suggests that species from different regions came together after population divisions and then expanded their ranges.
• The center of accumulation model suggests that species from scattered areas gathered in the Coral Triangle, creating a diverse population.

Some species found in the Coral Triangle include:
– Table coral Acropora latistella
– Pink soft coral
– Nembrotha kubaryana
– Christmas tree worms (Spirobranchus giganteus)
– Parrotfish
– Harlequin ghost pipefish
– Anemonefish (Amphiprion ocellaris)
– White-eyed moray eel (Gymnothorax thyrsoideus)

Threats

The Coral Triangle is an area where human activities, such as population growth, economic development, and international trade, are increasing quickly. These activities, along with changes to habitats, overuse of natural resources, and climate change, are causing problems for the environment. Issues like competition between species, fishing practices, pollution, debris, dredging, sunscreen chemicals, climate change, ocean acidification, disease, diving, rising sea levels, and temperature increases are affecting coral reefs.

Ocean acidification is a major threat to coral reef ecosystems. Because the Coral Triangle has a wide variety of plant and animal life, damage to coral reefs will affect many areas. This is because coral reefs are essential for coastal environments. Ocean acidification starts when carbon dioxide from the air dissolves in seawater, reducing calcium carbonate levels. This leads to more erosion and faster breakdown of coral structures. The Coral Triangle usually has clear, nutrient-poor waters that allow sunlight to reach algae living inside coral, which helps the coral grow. However, in West Maui, Hawaii, coral reefs are exposed to water that is rich in nutrients and has a lower pH. This water also has nitrate levels 50 times higher than normal. These conditions reduce the ability of corals to build their structures and increase erosion. Studies using nitrogen isotope measurements show that pollution from land can worsen the effects of ocean acidification by increasing erosion caused by excess nutrients. These conditions may cause coral reef ecosystems to collapse sooner than expected.

The rich biodiversity and productivity of the Coral Triangle are being harmed by poor management of the ocean, such as coastal development, overfishing, and harmful fishing methods. Lack of political action, poverty, high demand for seafood, and local disregard for endangered species are also contributing factors. Climate change, including rising ocean temperatures, acidification, and sea level rise, is causing coral reefs to bleach in large numbers, which harms important ecosystems. Around 120 million people live in the Coral Triangle, and about 2.25 million rely on the ocean for their livelihoods. These threats are risking people’s jobs, economies, and the future supply of species like tuna. Research shows that coral cover in the region has declined significantly. However, a 2021 report noted that coral reefs in the Coral Triangle have shown resilience during major bleaching events. The Global Coral Reef Monitoring Network (GCRMN) reported in 2021 that the East Asian Seas, which include the Coral Triangle, had higher coral cover in 2019 (36.8%) compared to 1983 (32.8%), despite experiencing large-scale bleaching in the 2010s. Data also shows that algae cover in the East Asian Seas has decreased, leaving five times more coral than algae on these reefs.

Marine resources are a key source of income for people living in the area. Losing these important coastal ecosystems would have major consequences for communities and economies.

Conservation

The Coral Triangle is the focus of important conservation work by governments in the area, nature groups like the World Wide Fund for Nature, The Nature Conservancy, and Konservasi Indonesia, and organizations that provide funding, such as the Asian Development Bank, the Global Environment Facility, and USAID.

In August 2007, Indonesia’s President Yudhoyono suggested a group of countries working together to protect the region’s marine and coastal resources. This group included Indonesia, Malaysia, Timor-Leste, Papua New Guinea, Solomon Islands, and the Philippines. The group was later called the Coral Triangle Initiative on Coral Reefs, Fisheries and Food Security (CTI-CFF).

The CTI-CFF has a plan to:
1. Identify and manage important areas of the ocean.
2. Use methods that protect fish and other marine resources while managing them.
3. Create and manage protected ocean areas.
4. Develop ways to adapt to the effects of climate change.
5. Improve the status of species that are at risk of disappearing.

The long-term goals of the CTI-CFF include:

Scientific support for managing resources comes from universities and research institutes. On February 28–March 1, 2017, the first meeting of the CTI-CFF University Partnership took place in Manado. The meeting aimed to:
1. Create a plan for how universities and research institutes can work together and choose a leader for the partnership.
2. Develop programs and funding for education, research, and outreach that help achieve the goals of the CTI-CFF.
3. Find ways to improve the work of groups like the Regional Secretariat, Technical Working Groups, and the National Coordination Committee.

The results of the meeting included:
1. A plan for how the CTI-CFF University Partnership will work.
2. Three programs: (a) a special education program to train people in managing the Coral Triangle’s ecosystems and help Timor-Leste improve education in fisheries and marine science; (b) nine research projects on important topics; and (c) outreach activities.
3. The leader of the CTI-CFF University Partnership for 2017–2020 is Prof. Dr. Grevo Gerung from Sam Ratulangi University in Indonesia. The next meeting of the CTI-CFF University Partnership will be held in 2018.

Delineation

The main factors used to define the Coral Triangle are:

• High biodiversity, including over 500 coral species and many types of reef fish, foraminifera, fungi corals, and stomatopods, along with diverse habitats.
• On the oceanography side, the Indonesian Throughflow region (ITF) plays an important role in the Coral Triangle. The ITF has input ranging from −10.7 to −18.7 Sv and output ranging from −2.6 Sv to −9.8 Sv. It helps regulate global ocean circulation, the climate system, and ecosystem sustainability. The region has complex geography and circulation patterns, including changes in water movement, sea surface temperature, and mesoscale variability. Seasonal and yearly changes in water mixing show that the Coral Triangle is influenced by ENSO and the Asian-Australian monsoon system.
• There are ten key passages in the Coral Triangle. These are: (1) Makassar Strait, (2) Lifamatola Strait, (3) Lombok Strait, (4) Ombai Strait, (5) Timor Passage, (6) Luzon Strait, (7) Karimata Strait, (8) Mindoro Strait, (9) Sibutu Strait, and (10) Torres Strait. The current system in the Coral Triangle is affected by the North Equatorial Current (NEC), North Equatorial Countercurrent (NECC), South Equatorial Current (SEC), South Equatorial Countercurrent (SECC), Mindinao Eddy (ME), Halmahera Eddy (HE), and New Guinea Coastal Current (NGCC).

There is a lot of overlap between the areas defined by high coral biodiversity (more than 500 species) and the areas with the greatest biodiversity of coral reef fish.

Media

The 2013 documentary film "Journey to the South Pacific" shows how people are working to protect the Coral Triangle while also showing life on the islands.