Status of Koh Tao’s coral reefs

Hin Wong Bay, 2013

Beautiful Acropora corals growing in Hing Wong Bay, Koh Tao, 2013

How are the corals on Koh Tao doing? There is no simple answer to this question. As divers and stewards of the reefs of Koh Tao we observe many changes in the ecosystems of the various bays around the island, both for better and for worse. Sometimes we tend to focus our memories on the best spots we have visited, or think back to a disaster like the coral bleaching event in 2010. Either way, the metal perception that we have of the reef may not be the entire picture, and this is why it is vital to have accurate and long-term data through regular monitoring.

In 2006, the Ecological Monitoring Program was started by the CPAD Foundation and Dr. Wayne Phillips of Mohidol University International College. It was in that summer that the program was established and taught to Chad and Dev at New Heaven. Since that time, the program has evolved to include more indicator species and data collected, more locations, and a manual. Plus certifications in the program by both SSI and PADI. To date, data is available from 14 locations around the island, for 7 years. This data is used to direct the projects we complete both at the NHRCP, and also with the Save Koh Tao Group and The Department of Marine and Coastal Resources.

Recently, one of our interns, Margaux Hein, started her master’s degree at the James Cook University in Australia. As part of her Master’s work, she has taken it upon herself to analyze some of the years of EMP data and look for trends in the genera of coral different locations based on the levels and types of stresses present. She has found some quite remarkable correlations in her analysis, which we hope will allow us to better direct our policy and management decisions here on the island.

One of the findings we are happy to see is that the average coral coverage in over half our reefs is between 25-50% which is ‘fair’ relative to the global average. One third of our sites had over 50% coral coverage, ‘rated as ‘good’ compared to the global average.  Furthermore, coral coverage seems to have recovered well since the bleaching event of 2010.

Often in our program we have mentioned that a genera of Foliose (plate-like) corals called Pavona tends to dominate areas with high amounts of stress (learn more about coral growth forms). This was based on what we could infer by the fact that there growth form easily sheds sediment and is prone to asexual fragmentation through breakage. Plus we thought we saw lots of them in areas that had a lot of development or run-off. In Margaux’s paper, she showed that there is in fact a very strong correlation in the ratio of branching Acropora to the Pavona between the ‘high’ stress and ‘low’ stress sites (see graph below). Clearly in the data Pavona persists well in disturbed areas, and Acropora is abundant only in reefs with low chronic stresses. This is important in not only the management of reefs, but also in fisheries, as Acropora  corals are more structurally complex than Pavona and will act as better nurseries for a wider range of fish species.

Coral genera of Koh Tao

The most abundant coral around our island was Acropora, followed by Porites and Pavona. With the ‘low’ use sites showing a higher variation in the genera present, and the high use sites dominated primarily by Pavona and Porites. Interestingly there is a clear split between the abundance of brooding corals versus broadcasting corals between the ‘high’ use and ‘low’ use sites, something which we may have to investigate further in the future.

Koh Tao Coral Genera

The paper sets up a solid baseline on which to compare future changes in the reef health, abundance, or diversity. Furthermore, the paper helps us to better understand the changes on our reefs, and what decisions and actions must be taken by the community and government to protect and preserve the reefs of Koh Tao.


Margaux’s full paper; An Assessment of the State of Koh Tao’s Coral Community from 2006-2012, is available for download in the Publications and Student Papers section of our website . But stay tuned for more from her, as in August she will return to complete her Master’s study concerning the state of reefs in Marine Protected Zones on Koh Tao.