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The Coral Triangle - Oasis of life
Written by Alex Rose, M.Sc.   

The Coral Triangle is the only place on Earth that rivals the biodiversity of the Amazon Rainforest in both species richness and environmental importance. This article will cover the amazing biodiversity in this part of the world, some of the unique and important creatures that live there, and the importance of protecting this environmental treasure.

About the Coral Triangle

The Coral Triangle covers approximately 2.3 million square miles of ocean and encompasses six countries in the Indo-Pacific: Indonesia, Malaysia, Papua New Guinea, the Philippines, the Solomon Islands, and Timor-Leste. An unbelievable amount of biodiversity is condensed into less than 1% of the world's ocean surface area: The Coral Triangle (CT) is home to one-third of the world’s coral reefs, 75% of known coral species (~600 species of corals), nearly 3,000 species of fish, half of the world’s seagrass and marine mollusk species, 75% of known mangrove species, six of the world’s seven species of marine turtles (green, hawksbill, olive ridley, leatherback, loggerhead, and flatback), and more than 22 species of marine mammals.

The Coral Triangle

Figure 1: Map of the Coral Triangle. (Image: Google Earth/Tim Wijgerde).

The Coral Triangle has been an evolutionary hot spot due to the combination of light, high water temperature, and strong, nutrient-rich currents from the collision of the Pacific and Indian oceans. The seasonal influx of nutrients from these deep ocean upwellings along with equatorial sunshine and warm seas results in an abundance of phytoplankton and zooplankton. This provides nourishment for corals, fish (larvae) as well as migrating giants like manta rays and whale sharks. The presence of coral reefs and mangrove forests buffers the effects of storms and tsunamis on coastal communities of the Coral Triangle. The abundant resources of the Triangle directly support the livelihoods of 126 million people as well as benefiting millions of others worldwide. The total annual economical value of natural habitats in the Coral Triangle including coral reefs, mangroves, and seagrass beds is an estimated US $2.3 billion. Not to mention the ever-growing business of ecotourism, as well as the multi-billion dollar tuna industry that is directly supported by the spawning and nursery grounds of the Coral Triangle, making it even more obvious why their protection is paramount. Many commercially important species of fish inhabit these waters, making them an ideal place for local people to live and work.

"An unbelievable amount of biodiversity is condensed into less than 1% of the world's ocean surface area."

Coral Triangle Species

The commercial fishing industry of the Coral Triangle generates US $3 billion in income annually and supports millions of people in many costal villages. Coral reefs, mangroves and seagress beds are crucial breeding grounds for many marine creatures, including several commercially important species such as yellowfin tuna, bigeye tuna, skipjack tuna, Napoleon wrasse, and bumphead parrotfish. Without these nurseries for large pelagic fish species, there would be nowhere for adults to spawn or for the fry and juveniles to grow and eventually reproduce, making the continued existence of these species impossible.

A group of Amphiprion clownfish

Figure 2: A group of Amphiprion clownfish scurrying around in their host anemone (Heteractis magnifica, photograph: Alex Rose).

 The Coral Triangle is also known for its incredible array of creatures that are endemic to the area. Some of the most unique and unbelievably-coloured animals are the nudibranchs. Nudibranchs, meaning “naked gills” (Latin nudus, naked, and Greek brankhia, gills), are bilaterally symmetrical gastropods that are often poisonous and exhibit aposematic colouration to deter predation. They are hermaphroditic and typically carnivorous; most nudibranch species have extremely specialised eating habits and consume one or a few species of sponges, hydroids, corals, anemones, flatworms, tunicates, barnacles, or even other nudibranchs. There are nearly 1400 species of nudibranchs and sea slugs, collectively called opisthobranchs, that have currently been identified in the Indo-Pacific region. These beautiful creatures seem to have utilized every colour in the spectrum of visible light to decorate their flamboyant bodies.

Chromodoris annae

Figure 3: A nudibranch, Chromodoris annae, cruising along coral rubble in the Philippines in search of a sponge to eat (photograph: Alex Rose).

There are many species of mantis shrimp that inhabit the Coral Triangle, but eight of them are endemic to the region. Stomatopods are fascinating creatures with amazing eyesight and an incredibly fast attack strike. They can range in size from 2 cm (about ¾ of a inch) to over 30 cm (1 ft) in length, but most mantis shrimp species which inhabit the Coral Triangle are extremely large. For example, the stomatopod Lysiosquillina lisa which is commonly found in the Philippines can grow to a length of 25 cm (10 inches) or more. It has huge spearing claws, as opposed to smashing claws, that allow it to eat fish larger than itself.

Lysiosquillina lisa

Figure 4: A large spearing mantis shrimp in the Philippines, patiently waiting in its burrow to capture a fish (photograph: Jeni Tyrell).

One of the most amazing creatures that can be found in the Coral Triangle is the Flamboyant cuttlefish (Metasepia pfefferi). This amazingly colourful cephalopod grows to a maximum total length of 12.5 cm (5 inches), hunts fish and crustaceans for food, and has toxins in its skin and musculature. It is currently the only known toxic cuttlefish; its toxin is as potent as that of the deadly Blue-ringed octopus (genus Hapalochlaena). These creatures also have the ability to rapidly change colour. They can do this by utilising extremely high densities of skin pigment cells (chromatophores and leucophores) and reflective cells (iridophores). Two hundred pigment cells per square millimeter of skin allow the Flamboyant cuttlefish to produce many different colours and patterns in rapid succession, in order to communicate with conspecifics, camouflage themselves from predators, or warn intruders of their toxicity.

This melting pot of biodiversity contains many creatures that exist nowhere else in the world as well as commercially valuable species that are found throughout the world’s tropical waters. In the coming years, it is extremely important that the Coral Triangle is protected from further damage and allowed to recover from many years of neglect and abuse. Forty percent of the Coral Triangle’s coral reefs have been lost over the last forty years and the resilience of the Coral Triangle is beginning to diminish as a result of many anthropogenic changes, some of which will be discussed in the next section.

Metasepia pfefferi

Figure 5: A Flamboyant cuttlefish in a shallow seagrass bed near Apo Island, Philippines (photograph: Alex Rose).

"There are many issues threatening the existence of the Coral Triangle as well as its people, such as global climate change, ocean acidification, sea level rise, unsustainable coastal development and fishing practices."

Saving the Coral Triangle

The Coral Triangle is a place of unmatched biodiversity, beauty, abundance and importance that has unfortunately not garnered the respect it deserves. There are many issues threatening the existence of the Coral Triangle as well as its people, such as global climate change, ocean acidification, sea level rise, unsustainable coastal development, and unsustainable fishing practices including over-fishing, high levels of bycatch, and blast and poison fishing. Fortunately, steps are being taken by the governments of the Coral Triangle nations to protect this part of the world against abuse and destruction.

Following are some of the primary issues that are detrimental to the survival of the Coral Triangle:

1: Climate change is directly responsible for a rise in sea-surface temperature in the Coral Triangle, which is significant enough to cause increased frequency and severity of coral bleaching events. One of the most devastating coral bleaching events occurred during the 1997-1998 El Niño Southern Oscillation (ENSO), which damaged or destroyed nearly 20% of the coral reefs in Southeast Asia.

2: Ocean acidification is the result of increasing levels of carbon dioxide in the atmosphere being absorbed by the ocean causing a decrease in pH. A slightly more acidic pH results in the dissolution of the skeletons of calcifying organisms such as hermatypic (reef-building) corals, shellfish, and many species of algae. This could have dramatic negative effects on the composition of oceanic ecosystems and the existence of coral reefs.

3: A sea level rise of as much as 50 cm in the next forty years is predicted from current scientific data. This would result in loss of land, the inundation of coastal water supplies and increased damage from storms due to the lack of a coastal buffer.

4: Extremely high population densities and growth rates have fueled the rapid development of coastal areas in unsustainable ways. Coral reefs and mangroves have been removed to make way for the rapid expansion of urban and agricultural activities along the coastline; coral reefs have also been mined to make cement building materials to expand cities. Unchecked coastal development has also led to extreme pollution from agricultural runoff and sewage.

The effects of blast fishing

5: Overfishing currently occurs at approximately 64% of reefs in the Coral Triangle. With ever-increasing local and international pressure to take more from the sea, many fisheries already have or are threatened by collapse. A major issue associated with overfishing other than the taking of too many fish, is bycatch. Bycatch refers to all the animals caught accidentally, which often includes other fish species (common and endangered), turtles, sharks, marine mammals, and sea birds. Some methods of fishing such as trawling and long-lining result in bycatch rates of 50% or more with the unwanted animals tossed back into the water dead or dying. Blast and poison fishing also threaten about 50% of the Coral Triangle. Blast fishing utilizes explosives to stun fish while poison fishing makes use of potassium cyanide to impair or kill fish prior to collection. Both of these methods are extremely destructive to coral reefs and all their inhabitants.

Figure 6: The effects of blast fishing on a reef in Indonesia (photograph courtesy of NOAA).


While these numerous issues may seem insurmountable, it is absolutely essential that this place of biological wealth is preserved. Measures are currently being taken, such as the Coral Triangle Initiative (CTI), to address the problems of climate change, unsustainable development and fishing practices, pollution, poverty, and loss of important coastal ecosystems, and to put in place an action plan to save the Coral Triangle and its people.

It is encouraging to see the leaders of the six Coral Triangle nations come together to sign a commitment to protect their invaluable marine resources and the well-being of their citizens. Unfortunately, many of these problems reach much farther than just the Coral Triangle. The waters of the world are seeing the ill effects of global climate change, ocean acidification, pollution, unchecked population growth and coastal development, overfishing, illegal fishing and high rates of bycatch. These global problems cannot be solved by one small group of nations uniting to fight for a better future, but by many world leaders following the guidelines put forth by the Coral Triangle Initiative to ensure a better future for the people of the world and our future generations.

"The Coral Triangle is a place of remarkable diversity and immeasurable importance and is considered top priority for conservation along with the Amazon, Arctic, Galapagos Islands and Madagascar."


The Coral Triangle is a place of remarkable diversity and immeasurable importance and is considered top priority for conservation along with the Amazon, Arctic, Galapagos Islands and Madagascar. Continued research and education foster an understanding of these amazing places as well as an appreciation for their role in the biodiversity and sustainability of our planet. 

Destructive bycatch

Figure 7: A trawling boat in the Indo-Pacific fishing for orange roughy, Hoplostethus atlanticus. There is one orange roughy in the top lefthand corner. (photograph courtesy of RightBite program, John G. Shedd Aquarium).


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