Tracking the trajectory of coral reefs in the Andaman Islands

An edited version of this article was first published in the Hornbill, Bombay Natural History Society Magazine, April-June, 42-45.

An example of a resilient reef with high coral cover, dominated by species likely resistant to coral bleaching_Vardhan Patankar
An example of a resilient reef with high coral cover, dominated by species likely resistant to coral bleaching

Corals are some of the simplest, yet most complex organisms on the planet. Primitive, yet amazingly modern. Smaller than a size of your nail or bigger than your car. Unbelievably resilient, yet dramatically vulnerable.


I fell in love with the reef ecosystem when I observed colourful and vibrant reefs in the Andaman Islands fifteen years ago and they have been my driving force ever since. Although I was involved in documenting the post-tsunami damage to the reefs and their subsequent recovery during my initial years of research, the real quest to study the reef ecosystem started eight years ago, in the summer of 2010 to be precise, when I had the first inkling to the mass coral bleaching phenomenon. Until then I had only heard of coral bleaching, which occurs when the symbiotic dinoflagellates called as zooxanthellae (a type of microalgae)  are lost from reef-building invertebrates; without the algae, corals lose their colour and a source of energy and die or turn bleached (white). But what my colleagues and I observed was far worse than our imagination. We spent the next year documenting the impacts of the bleaching phenomena. Altogether, we surveyed seventy-five sites along fifty-one islands across the length and breadth of the islands. Every site was different in terms of its location, percent of live coral cover, and overall fish species composition, yet they all had a few usual suspects of corals and fish. Surveying reefs of north Andaman felt like as if we were swimming over cemetery of corals. Whereas in South Andaman and Nicobar archipelago only a few corals had bleached. Why certain reefs didn’t get bleached whereas other bleached kept us baffled.

A bleached colony of Acropora sp

In subsequent years, we continued monitoring these sites and what we observed took us by surprise. Many sites had succumbed to rubble and did not recover, whereas others hardly bleached and recovered fully. There appeared to be a lot of variation on how much coral cover is affected by physical and biological disturbances and the real-time question that emerged was how quickly coral communities can recover after disturbance. This is an age-old question, that has intrigued many including me, and thus, I have been assessing reefs of the Andaman Islands with the aim of understanding what makes certain reef resilient, others resistant whereas a few susceptible in the face of repeated disturbances. A resilient reef is better able to recover from stress events like bleaching and storms. They are like our immune system. A person with better immunity can recover quickly from illness and viral infections such as cold, whereas a person with low immunity can take a long time to recover.

After reviewing and collating past information, it was clear that the Andaman and Nicobar reefs have been grappling with massive coral mortality since time immemorial. As per the documented records, the Andaman Islands were hit by three tsunamis, the most recent and dramatic being the tsunami of 2004, and repeated coral bleaching has affected the island reefs. Just when reefs were beginning to recover, another natural catastrophe, the El Niño that warms the water in the equatorial Pacific and affects global weather impacted corals of the world, including those located in the Andaman Islands.  However, we are not the only ones going through the crisis – reefs of several countries have been affected by the 2016 bleaching event, which is also believed to be the longest and most intense bleaching event in history.  A recent study predicted the local extinction of many reefs in the next 50 years. Other than natural catastrophes, many other types of disturbances or stresses can kill corals including cyclones, disease, pollution, overfeeding of coral by crown-of-thorn sea star, many of which are human induced.

All host anemones are susceptible to bleaching, and during the peak of heat year there could be reductions in the abundance of both the anemones and their resident clown fish
All host anemones are susceptible to bleaching, and during the peak of heat year there could be reductions in the abundance of both the anemones and their resident clown fish

People often ask that if disturbance and recovery of corals are part of the natural coral reef ecosystem, then why bother studying reef resilience? My answer is that the frequency of disturbances is exponentially higher than previously known, and monitoring coupled with active management is the only hope to save them. After major natural catastrophes, there are some corals that survive the heat stress, recover quickly, and recolonize the dead reefs. Imagine if we have basic ecological data collected as part of long-term monitoring programs to better predict which reefs might bleach, which ones will survive, and which ones will bounce back and recover quickly. If we had this information, wouldn’t we make sure that these reefs were adequately protected? And wouldn’t that enable the custodians of marine protected areas to make better decisions to reduce as much “man-made” stress as possible in order to give these more resilient reefs a stronger chance of survival? This is why understanding reef resilience is important.

In order to do this, we have selected 10 sites and at each site, we collect data on a range of variables that are known to confer resilience of the reefs. My colleagues, Zoya Tyabji and Nairika Barucha collect data on invertebrates and coral genera found on different reefs and their relative abundances, whereas Tanmay Wagh and I collect data on reef fish and benthic categories. In addition, in order to understand how herbivore fish aid in the post-disturbance recovery of corals, Tanmay has set-up experiments to understand how herbivore fish maintain the coral-algal balance on reefs.

Our sampling team

The information we are collecting is consistent with monitoring data collected by different organisations across the world such that our data contribute to the global effort on understanding reef resilience. As the ocean temperatures keep rising, we know that it is not only the corals that suffer from rising ocean temperature. Bleaching diminishes the reef in ways that we are just beginning to understand reducing the overall health and stability of the entire ecosystem.

IMG_20180202_123006.jpgFor the majority of reefs in the Andaman Islands, there is limited information on the condition and health of the reefs. A few recent studies suggest that understanding and managing local processes e.g., local hydrodynamics, ecological and physical factors, fishing pressure, could play an important role in the recovery of coral reefs. We are now analysing a massive dataset and trying to solve the jigsaw puzzle through the lens of reef resilience and creating some sort of roadmap for how these reefs will respond in the face of repeated disturbances. The hope is that the data we are collecting can be used by the Andaman authorities to help make decisions about where to concentrate their resources to maximize the efficiency of protecting the reefs.

Though doom and gloom of tsunami and bleaching is a reality, there is a reason to be optimistic about the reefs. Rather than writing refined obituaries of coral reef degradation, it is also important to highlight success stories of reef resilience. Our preliminary findings indicate that at many reef sites reefs are remarkably resilient. These areas should get all attention from reef managers. A good start is to strengthen existing protected areas and to realise that the people’s livelihoods in the Andaman Islands are directly or indirectly linked to the reefs’ resilience. Managing coral reefs is complex—it’s unsteady balance of ecosystem, science, politics, and economics. The current situation demands complicated solutions, especially since it involves dealing with global climate change, reducing our carbon footprints and the lives of thousands who are dependent on reefs. A thorough understanding of different factors that are important for coral reefs can give us a way beyond the easy hand-washing, nothing-can-be-done, attitude. By recognizing that coral reefs and our societies are inherently coupled, we can evolve better strategies to manage them that are ecologically sound, as well as socio-economically equitable.


Published by Vardhan Patankar