Threats to Reef Health

The problems that are facing coral reef ecosystems are many, from terrifying global threats to more manageable, but often times just as deadly local threats. Coral reefs have been facing massive declines since the Industrial Revolution, and most of this can be traced back to the rapid rate at which we’ve caused our planet’s climate to change, a rate at which corals can no longer keep up with. As a species, humanity has changed the composition of our atmosphere to such an extent that we now call the time we’re living in the Anthropocene, which is defined as an age where our own actions have been the dominant influence on climate, and the climate is changing so quickly that many ecosystems are having a hard time keeping up. Corals are perhaps the greatest tells that we have of this. As our oceans’ sea surface temperatures are becoming warmer and warmer, we’re begin to experience phenomena on coral reefs that were never before observed by mankind.

Rising Sea Surface Temperatures

While coral reefs have bleached naturally in certain parts of the world, in 1998 we witnessed one of the first Global Bleaching events that was ever recorded, an event where coral reefs lost their colour across massive geographic regions and eventually the planet. In this single event, it’s estimated that nearly 50% of coral reefs were wiped out and here on Koh Tao it brought about the collapse of Shark Bay’s coral reef ecosystem. Once corals have lost their colour, it means that the colony has lost its photosynthetic microalgae (zooxanthellae) and can no longer produce oxygen and glucose for itself causing it to starve. Until temperatures cool allowing the coral to gain back these microalgae, the coral stands a very high chance of dying. Since that dramatic event has happened with increasing frequency, often times coinciding with the El Nino Southern Oscillation, and the latest global bleaching event that began in 2014 and stretched into 2017 was one of the worst to date.

Ocean Acidification

Carbon Dioxide is a well-known greenhouse gas that’s being released into the atmosphere through our own activities and is driving much of the warming our planet is experiencing. Our planet’s oceans try to balance out the amount of carbon in the air and the carbon that they store by soaking it up, making them our biggest sink for CO2. Unfortunately, Carbon Dioxide react with water to form carbonic acid. Our oceans have a pH around 8.2, making them alkaline, but this carbonic acid is causing our oceans pH to drop at an alarming rate. It’s predicted that by the end of the century it could drop to a pH of nearly 7.6, near acidic levels, and it will continue to drop well after that. Life in our oceans has evolved under alkaline conditions and depend on it for their survival. If our planet’s oceans drop below a pH of 7 and become acidic, most forms of life will be affected one way or another, but especially those that depend on calcium carbonate for their survival. Coral produce calcium carbonate skeletons, which reacts with carbonis acid causing them to break down over time.

Water Pollution

Plastic is perhaps the most obvious form of pollution in that it’s the most visible. Plastics have already become startlingly abundant in our oceans and an estimated 8 million metric tons of new plastic will be washed out into our oceans every year. Cleanups are often advertised by other dive schools as a conservation dive, but we believe that every dive a diver should be on the lookout for marine debris to remove. As long as our team is in the water, we’ll be cleaning up the waters around Koh Tao. Unless we all adopt this attitude while visiting our oceans and curb our single-use plastic addiction, problems this large will continue. 


All things flow into the sea. This saying is certainly true when it comes to human waste which is rich in nitrates. If water is not treated properly before it reaches the ocean, these nutrients in our waste help organisms that compete with coral, like algae, sponges and tunicates. These competitors can outgrow slower growing coral and can shade them, resulting in death. Many coral reefs across the globe are collapsing, as  mounting threats are creating the conditions where macro algae are replacing them, our own local example being Shark Bay in 1998. Once macro algal growth has taken over on a reef, to return to a coral dominated community can take decades if not centuries even under ideal conditions.
Even more deadly is when fertilizers running off of land being used for agriculture makes it into our oceans. These fertilizers can lead to harmful algal blooms, which are most commonly made up of primitive bacteria. These bacteria produce noxious toxins that can harm marine life in the areas where these prokaryotes are blooming. Not only do they produce toxins, they also die, and their biomass is so great that it often times will begin decomposing in a way that produces an even greater volume of harmful chemicals. This process kills out all life in the area and the space becomes toxic and can take years before life can begin to move back into the area. This process is known as anoxia or eutrophication and creates massive dead zones across our planet.  

Irresponsible Fishing

Fishing is an incredibly important part of many coastal cultures and many locals here in Thailand rely on these resources to help sustain them and their families. When done irresponsibly however, the effects can be devastating to both the oceans and local economies. Irresponsible fishing techniques like trawling, ghost nets, long-lining, fishing cages, and spearfishing to name a few are incredibly damaging and wasteful to our oceans, and on a coral reef they can destroy the natural balance of these fragile spaces. Overfishing can lead to the collapse of fish stocks which can take decades to recover, if ever. The Save Koh Tao group helped push policy through that protects much of our island and drastically reduced these harmful practices.

Physical Disturbance

Anchor dropping is perhaps one of the most obvious and needless forms of destruction on coral reefs. In many parts of the world anchors are dropped every time a boat moors up at a reef which takes a second to do but can destroy hundreds of years of coral growth just as quickly. On Koh Tao we’re working with local authorities and branches of government to bring mooring lines to the reefs around our island, allowing boats to tie up to permanent lines found on each dive site stopping the need for anchor dropping.
Even something as simple as standing on a coral can kill it though. Corals are a very sensitive, thin layer of tissue that covers the large and beautiful limestone structures that they have secreted over their lives. Breaking and scraping this tissue can open them up to bacterial infections and disease which can kill an entire colony.

Erosion and Sedimentation

An estimated 40% of the world’s population lives within 100 kilometers of the coast. All of these people living so close to the ocean means an incredible amount of development. As we continue to build along our shorelines, we displace huge volumes sediment and soil, all of which flows out into the ocean. On coral reefs these sediments reduce visibility in the water column as they stay suspended there, making it difficult for coral to get the light they need to photosynthesize. Eventually these sediments settle, burying the coral underneath them ensuring that they can no longer access light or even water to feed. Koh Tao has developed rapidly since tourism first started in the 1980s, and with it so too has rates of coastal erosion and the sedimentation across the coral reefs.

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    Koh Tao, Surat Thani
    84360, Thailand
Copyright 2016
New Heaven Reef Conservation Program