Often we are asked, How are the reefs on Koh Tao doing? Although it is a simple and straight forward question, there is no simple answer. Over the year we have see both sides of the coin of coral health. In some areas we have seen incredible development and regrowth of the reefs, and in others we are still witnessing a continued decline.
Generally, we will have several years of great growth despite all of the human activities going on, and then experience some major event which puts even more pressure on already stressed reefs. On the short term things can be either amazing or devastating, but what about the long term health and trajectories of the reefs on Koh Tao?
The history of Koh Tao’s reefs is scarce, but some information can be found in scientific publications (a list of the papers can be found at the end of this article). One of the oldest papers discussing Koh Tao is from Len Garces, who in 1992 published a report on the management of coral reefs in Thailand. His report outlined the ineffectiveness of local governments and agencies in managing the reef resources around the Samui Archipelago, stating “the government agencies poor coordination, both at the local and national levels, prohibits effective action in the conservation of coral reef resources.”
Few papers are available mentioning the reefs of Koh Tao until 2006, in a report by Yeemin et al. discussing reef restoration projects in Thailand. In the report, the authors give an overview of the reefs of the Andaman and Thai Gulf, stating that for the Gulf, “16.4% of the reefs were rated ‘excellent’, 29% good’, 30.8% ‘fair’, and 23.8% ‘poor’” (see figure at right). Furthermore, the report stated that over a 5 year period leading up to the report, the coral coverage on Koh Tao declined by 17%, largely due problems related to tourism and development, including dropping of anchors. The report also states that the mass coral bleaching event of 1998 was devastating to the island, but that a 2002 survey clearly showed signs of recovery and recruitment.
One of the most complete ways to tell the current story of the reefs of Koh Tao is through the papers and reports completed by our students and staff. In 2010, Robbie Wetterings, then an intern at the NHRCP, integrated remote sensing and locally collected data to compile a threat map for the reefs of the island (see map at left). His research showed that the forests of Koh Tao have largely been replaced by coconut plantations and human settlements, in 1975 96% of the primary forest was still intact, but that fell to 79% by 1994, then 61% by 2005, for a total loss of 622 hectares. This loss of primary forest brought with it high amounts of sedimentation, erosion, and reduced water clarity, all factors which decrease the resilience of our coral reefs. In the worst cases, whole reef ecosystems have been lost, such as in Tanote Bay as outlined by Larpnun et al. in 2011.
The development of terrestrial areas often leads to a decline in water quality due to a process known as eutrophication. Corals thrive best in waters which are clean and nutrient deficient. If more nutrients are introduced to the reef ecosystem, this does not benefit the corals in any way, but it does however benefit marine plants – Macro-Algae. Macro-algae is always in competition with corals, and if given an advantage, can quickly overgrow the corals or prevent coral larvae from settling. The first of our students to investigate this effect on Koh Tao was Lena Franke in 2009.
In 2010, Koh Tao experienced another mass bleaching event, which lasted for over 5 months, and at its worst 98.1% of the corals during an EMP survey were coded as bleached. Subsequently, up to 68% of the corals died in some of the shallow reefs, such as Chalok Ban Kao. The effects of this bleaching event can be found in reports by Chad Scott on the status of the reefs of Koh Tao 2010, or the publication in the Journal Corals Reefs by Dr. Bert Hoeskema and Chad Scott detailing the loss of fungia corals to predators after the bleaching.
More recent reports on the state of Koh Tao’s reefs can also be found in the great studies done by NHRCP interns and JCU master’s candidates Margaux Hein and Fanny Couture. Margaux looked at the health of the coral communities around Koh Tao in ‘high’ use versus ‘low’ use sites. And Fanny assessed the effects of benthic structure and human activities on the fish assemblages on Koh Tao.

The graph above shows the average coral coverage for selected sites on Koh Tao based on 368 coral reef surveys completed between April 2006 and May 2014. Coral Coverage declined, primarily in Tanote and nearby Ao Leuk, over 2006-2007 due to the construction of a large reservoir. Coverage increased until 2010, when mass coral bleaching reduced the island average from 41.2% to 27.1%. By 2014 reefs had recovered to their highest levels since 2009, but are now being impacted by another large bleaching event.
By 2014, we have accumulated over 8 years of monthly reef data through the Ecological Monitoring Program. As this dataset grows, it becomes more accurate and important in telling the story of Koh Tao’s reefs. We do our best to publish this data and use it to report with local government groups and stakeholders, such in our reports on Tanote Bay (2008), Tien Og Bay (2014), Ao Mao (2011), or Sai Nuan (2014).
The reefs of Koh Tao are some of the most diverse and abundant in the Gulf of Thailand. Yet like reefs all over the globe they are threatened by the local activities of humans and the global problems of climate change. If a simple answer to the question of ‘how are the reefs doing’ must be given, then it is unlikely to be optimistic. But it is also important to remember that they are not gone yet, and many people are fighting to protect and restore the reefs of Koh Tao. You can learn more about these actions in our Conservation Projects section, or come and help us understand and address these issues by enrolling in one of our conservation courses and internships.

Below you can see a complete list of the known English reports and publications for Koh Tao, and is provided as a list of resources for any students looking to complete a research study here on the island. If you have trouble finding any of the papers or reports on your own, please contact us. (papers in bold were authored, co-authored, or assisted in some way by the New Heaven Reef Conservation Program)


  • Mehrotra R and Scott CM (2015). Species inventory of sea slugs (Gastropoda: Heterobranchia) for Koh Tao, Thailand, with 25 first records for Thai waters. Marine Biodiversity. DOI: 10.1007/s12526-015-0424-7
  • Mehrotra R, Scott CM, Hoeksema BW. 2015. A large gape facilitates predation on salps by Heteropsammia corals. Marine Biodiversity. DOI: 10.1007/s12526-015-0379-8.
  • Mehrotra R., Scott CM., Rohrer JM., Hoeksema BW. 2015. Predation on a sacoglossan gastropod by a mushroom coral. Coral Reefs. DOI 10.1007/s00338-015-1285-z.


  • Romeo, L. (2014) Tracing Anthropogenic Nutrient Inputs Using δ15N Levels in Algae Tissue Koh Tao, Thailand. Master’s Thesis, MAS Marine Biodiversity and Conservation, CMBC, Scripps Institute of Oceanography, UCSD. 29 pp.
  • Scott CM., Mehrotra R., Urgell, P. (2014) Spawning Observation of Acanthaster planci in the Gulf of Thailand. Journal of Marine Biodiversity. DOI 10.1007/s12526-014-0300-x
  • Scaps P., Scott CM. (2014) An update to the list of coral reef fishes from Koh Tao, Gulf of Thailand. Checklist: The Journal of Biodiversity Data, 10(5); 1124-1133. DOI: 10.15560/10.5.1123.


  • Hoeskema, B.W., Scott, C.M., True, J.D. 2013. Dietary Shift in Coralivorous Drupella snails following a major bleaching event at Koh Tao, Gulf of Thailand. Coral Reefs Vol 32, Issue 2, pp. 423-428.
  • Nichols, R. 2013. Effectiveness of artificial reefs as alternative dive sites to reduce diving pressure on natural reefs, a case study of Koh Tao, Thailand. Bsc. Thesis in Conservation Biology, University of Cumbria, Cumbria, UK. Print.
  • Phongsuwan N., Chankong, A., et al. 2013. Status and changing Patterns on Coral Reefs in Thjaiand during the last two decades. PMBC, 18pp


  • Chavanich, S., Viyakarn, V., Adams, P., Klammer J., Cook, N. 2012. Reef Communities After the 2010 Mass Coral Bleaching at Racha Yai Island in the Andaman Sea and Koh Tao in the Gulf of Thailand. Phkut Mar. Biol. Cent. Res. Bull. 71: 103-110.
  • Hoeskema, B.W., Matthews, J.L., Yeemin, T. 2012. The 2010 Coral Bleaching Event and Its impact on the Mushroom Coral Fauna of Koh Tao, Western Gulf of Thailand. Phuket Mar. Biol. Cent. Res. Bull. 71:71-81.
  • Platong, S., Chaloem, S., Charoenmart K., et al. 2012. Strategic Plan: Integrated Coastal Management for Koh Tao. Center for Biodiveristy of Peninsular Thailand, Prince of Songkla University, Hat Yai, Thailand.
  • Yeemin, T., Mantachitra V., Platong S., Nuclear P., Klingthong W., Suttacheep M. 2012. Impacts of Coral Bleaching, Recovery, and Management in Thailand. Proceedings of the 12 International Coral Reef Symposium, Australia.


  • Larpnun, R., Scott, C.M., Surasawadi, P. 2011. Practical Coral Reef Management on a small island: Controlling Sediment on Koh Tao, Thailand. Catchment Management and Coral Reef Conservation. GCRMN. 120p.
  • Wetterings, R. 2011. A GIS-Based Assessment to the Threats to the Natural Environment on Koh Tao, Thailand. Kasetsart J. (Nat. Sci.) 45 743:755
  • Thomas, C.R., Heron, S.F. 2011. South-East Asia Coral Bleaching Rapid Response: Final Report. CSIRO, 20pp.


  • Hein, M. In Preparation. An Assessment of the State of Koh Tao’s Coral Community from 2006 to 2012. School of Marien Tropical Ecology, James Cook University, Queensland, Australia.
  • Phillips, W.N., Scott, C.M., Zahir, D. 2010. Community Monitoring and Assessment of the Reefs of Koh Tao, Thailand. Proceeding of the the 2nd Asia Pacific Coral Reef Symposium. Marine Biodiversity Research Group, June 20-24, 2010. Phuket, Thailand.
  • Satapoomin, U. 2000. A Preliminary Checklist of Coral Reef Fishes of the Gulf of Thailand, South China Sea. Phuket Mar Biol. Cet. res. bull. 48(1).
  • Saengrithorn, S., Kitworawut, P. The First Medium Wind/Diesel Pilot Project in Thailand. Provincial Electrical Authority, Bangkok, Thailand.
  • Scaps, P. 2006. Eight New Reocrds of Coral Reef Fishes from the Gulf of T8ailand, SOuth China Sea. Phuket Mar Biol. Cet. res. bull. 67: 53-62.
  • Scott, C.M. 2008. Loss of Tanote Bay: Analysis and Request for Assistance. Save Koh Tao, 6pp.
  • Scott, C. 2012. The Koh Tao Ecological Monitoring Program. Save Koh Tao Community Group, Koh Tao, Thailand. 109p.
  • Scott, C., Phillips, W.N. 2010. A Sustainable Model for Resource Management and Protection Achievable Through Empowering Local Communities and Businesses. Proc of RUIRC 2010, Bangkok, Thailand.
  • Yeemin, T., Sutthacheep, M., Pettongma, R. 2006 Coral Restoration Projects in Thailand. Ocean and Coastal Management 49:562-575.


  • Garces, L.R. 1992. Coral reef management in Thailand. Coral reef management in Thailand. Naga, the ICLARM Quarterly, 15(3), pp. 40-42.

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