Koh Tao's Reefs, A story through time.

By Rahul Mehrotra

Corals, and the reefs they create, are slow to grow and slow to develop relative to many other animals and habitats some of us may be accustomed to in our lives. They do share much in common, however, with the numerous high-diversity ecosystems that we know and love, both on land and in the sea. Like the savannah, they can host vast hordes of animals that graze and migrate; like rainforests, can host an astounding array of critters large and small; and like mangroves, they are adapted to dynamic coastal, often intertidal, conditions while acting as nurseries for an incredible diversity of marine and coastal life. These ecosystems also share a great many threats that have come to define much of our understanding of wildlife today. Chief among these is the scientifically proven, evidence backed, you-cant-just-pretend-it-doesn’t-exist fact of a drastically changing global climate, and the impacts it has on our incredibly diverse world.
The slow growing nature of these ecosystems requires long-term monitoring to tease out the ways in which they are changing in response to turbulent conditions. On the last day of 2017, we published a highly anticipated paper on the changes of the coral reefs of Koh Tao over almost a decade of study. In it, we highlight a number of intriguing shifts our island’s reefs are making, such as that on the whole, the average coral cover on the island has actually increased a little (by approximately 3%) over the years. Based on the cover of hard corals on the reef, all sites that were considered ‘Poor’ back in 2006 (i.e. those with less than 25% coral cover) improved to a ‘Fair’ level (25-50% cover) by 2014 and Hin Wong Bay improved, retaining its ‘Good’ status of over 50% cover. However, that’s about as good as the news gets. All sites that were considered ‘Fair’ in 2006 actually dropped in coral cover, and Sairee which had initially be classified as ‘Good’ actually dropped to a ‘Fair’ level. At an island that sees up to and over 500,000 tourists per year, largely revolving around the SCUBA industry, the reefs are not the only thing to feel the pressure from this intense development, with an estimated 42.8% of natural forest being lost to development by 2005 (up from just 3.2% in 1975). With the explosive growth rate of the tourism industry at the island, these consequences on both marine and terrestrial habitats have further degraded in the forthcoming years.
Evidence also shows the impacts of the 2010 bleaching event, the first such event that data was collected before, during and after the event. Coral cover dropped dramatically over forthcoming years after the widespread bleaching and sporadic disease of corals (which you can learn more about here) and the mass predation by Drupella snails (which you can read about here and here). Though there were signs of recovery by 2014, what the data doesn’t yet show were the impacts of the forthcoming 2014 and 2016 bleaching events that hit the island since then. Among the biggest and most important discoveries in the paper is the shift in overall community structure over the years, with more vulnerable coral genera such as Acropora, Astreopora, Diploastrea, and Turbinaria undergoing sharp declines while more resilient genera such as Pavona, Porites, and Fungiidae corals showing increased dominance. While this may seem like a positive step for the reefs of the island, this progress of succession has some startling impacts, namely the loss of diversity of more vulnerable corals and the overall homogeneity of reefs leading to fewer dominant species and an overall loss in total diversity. As our reefs become more homogenous, the number of species that can be hosted by our reefs will change and likely decline due to the reduced variety of host life and structure. Of particular note is the impact of the loss in structural complexity provided by corals such as the branching Acropora corals which have been strongly linked to supporting a high diversity of both juvenile and adult reef fish.
Vulnerable vs. resistant
Koh Tao is an island that is changing incredibly rapidly, faster than many reef-associated islands around the world. These changes on land and in the sea far outpace the rate of our reefs to keep up, and so naturally begin to lose out before they are able to adapt to these shifts. Ongoing protection, community awareness and involvement, and further monitoring efforts will allow a greater understanding of the reefs now, and the years to come, and will hopefully allow us to direct our efforts to better preserve the diversity that lives on our doorstep. After all, we are the stewards of our ecosystems and the hands that can change them, for better or for worse.
To read the paper in its entirety, for free, click this link here

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The year of the Blue Ringed Octopus

What has nine brains and some of the most potent venom in the world? The incredible Blue Ringed Octopus.

A favourite dive of many of our students, interns and instructors is when we head of into the unexplored soft-sediment areas around our island in search of new and exciting marine life. Whilst most divers are spending their time exploring the reef, we head off into deeper waters on the hunt for some of Koh Tao’s most elusive and unique marine life.

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Citizen science and its role in marine species ID on Koh Tao


Citizen science has been playing an ever-increasing role in data collection and ecological research worldwide. With advances in technology and communication these non-scientists have been able to provide invaluable information. It is something we have been doing here on Koh Tao since 2015 when we started our Sea Turtle ID program. The program has proven to be incredibly successful and has resulted in over 70 turtles around the island being identified, recorded, and named.

After the success of the Koh Tao Turtle Project, we decided to set up Koh Tao Whale Sharks - to collect photos that are used to identify whale sharks visiting Koh Tao and submit them to Whaleshark.org to be part of a global ID program. This project enables anyone who sees a whale shark to submit photos of their sighting, along with additional information about these amazing creatures.

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Coral Disease on Koh Tao

Diseases amongst corals are becoming more prevalent since records first begun in the mid to late 20th century. This is due to a multitude of reasons, but most significantly are the increased frequency and intensity of coral bleaching events, and pollution. These both are stressors to coral colonies and leave them susceptible to disease. Since 2010, we have been tirelessly keeping up with recording data of coral disease around our little island of Koh Tao, and this last year we intensified those efforts. We collect this data so we can better understand the etiology of coral diseases and to keep track of outbreaks, and hopefully be able to one day mitigate the problems they bring.

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New Heaven Reef Conservation Program