If you have yet to visit a coral reef, let me tell you, the underwater screensavers on your computer do not exaggerate. Despite the frequent and intense episodes of coral bleaching that have been taking place, postcard-perfect coral reefs still exist in a few parts of the world. Brilliantly coloured corals grow in three-dimensional staircases, giving you the illusion that you are seated in an amphitheatre watching schools of fish dancing to Four Seasons by Vivaldi.
This was exactly how I imagined coral reefs were after cursory research and before my SCUBA certification dive course in the Andaman Islands in 2013. The reefs I saw during my first dives were quite far from the visuals I had painted in my mind from watching films and YouTube videos. Instead of rich arenas of coral, I witnessed graveyards of coral. Interlocking pieces of twig-like coral fragments lined the ocean floor, covered with a thick, fuzzy layer of algae. There were still many live and vibrant corals, but I could not ignore the scale of coral death. We were diving in an ocean that only three years earlier had experienced one of the worst episodes of coral bleaching recorded in human history.
Despite the coral bleaching, I was immediately in love. It was still the most beautiful space I had ever seen, and swimming weightlessly with fish made me feel accepted by the ocean. Of the different corals known to live in the waters of the Andamans, the ones that I found markedly sparse were the branching kinds of Acropora. To see a vast, endless patch of live branching coral became a personal bucket-list item.
According to the extensive volumes of Corals of the World (2000) by JEN Vernon, there are approximately 180 species of Acropora in the Indo-Pacific and Caribbean oceans. Twenty per cent of coral species in the Andamans are thought to be Acropora. Acroporids are shallow-water coral colonies of tiny polyps encased in miniature stony calcium trees. These may have numerous radiating branches or grow flat like plates or the tops of tables. They need relatively clear water and access to sunlight as they depend on the symbiotic zooxanthellae algae that live in their tissues for food produced by symbiosis.
A global study conducted in 2021 estimated that around the mid-1900s, corals covered between 58-70 per cent of reefs globally. Since then, live coral has declined by half. Currently, 166 of the 180-odd Acropora species are on the IUCN Red List of Threatened Species, and populations of all but four of them are in decline.
Repeated bleaching episodes due to ocean warming in the past couple of decades show us that Acropora corals have a very low tolerance to heat. They are typically the first to die out during a bleaching episode, with mortality rates of at least 70 per cent, despite Acropora being some of the fastest growing corals. Many species of boulder corals grow their skeletons barely one centimetre each year, but acroporid growth rates can be between 10-30 centimetres in a year. After a coral bleaching calamity occurs, Acropora have the potential to recover rapidly and provide structure and shelter to other marine life. Yet, many reefs in the Andaman Islands seemed to have more dead than live Acropora.
Since 2015, I have worked as a dive guide at Havelock in the Andamans. I spent many hours diving at Nemo Reef, a popular shallow shore reef. From my understanding, this place seemed quite suitable for Acropora coral, but there were hardly any apart from the beds of old dead branches on the sand. I was thrilled every time I stumbled upon even the smallest Acropora colony. I would check on it every few weeks, monitoring it visually as it grew, but invariably, these young colonies would perish and become overgrown by algae.
During the year 2020, the first year of the COVID-19 pandemic, something unexpected happened at Nemo. During this time, routine life in the Andaman Islands had stopped. I had moved out of the Andamans but continued to visit every summer. I snorkelled at Nemo in the summer of 2021, after a gap of 12 months. The reef in the first 5-8 metres depth had transformed. It was now almost entirely covered by Acropora thickets, and I was finally witnessing these magnificent creatures come back to life.
Each summer after that, the shallows of Nemo looked more spectacular than the year before, like an endless sea of Acropora. It was unclear what resulted in this sudden bursting abundance in coral cover in one year. Was there an Acropora spawning episode in 2020 that we all missed because of COVID-19? Did juvenile coral colonies finally survive their challenging initial stages of development without getting smothered under sediment or taken over by algae?
Regardless of how it happened, it did appear that Acropora was coming back at Nemo and other reefs around Havelock. Dive instructors who have been exploring these waters for over a decade finally saw these reefs begin to look like they did before the devastating bleaching episode of 2010. The ecosystem was reassembling itself. There was chemical competition between adjacent colonies, the budding of corals from broken fragments, partnerships of corals with numerous species of crabs and fish, and predation by coral-specialist snails. By the time I visited in March 2024, a most esteemed group of fish folk had arrived at Nemo, the long-nose filefish (Oxymonacanthus longirostris). These are small and spectacular fish that exclusively hunt Acropora polyps and are closely tied to the health of these corals.
It was with all this positivity and optimism that I began a story about the fall and subsequent rise of Acropora. Tragically, as I write this story at the end of 2024, it appears that Acropora is declining once again. Prolonged ocean warming that began in early 2023 made its way throughout the Indo-Pacific and Atlantic oceans, reaching the Andamans by April 2024. By the last week of April 2024, water temperatures around Havelock had crossed 32 degrees C and felt unbearably hot even to us. One after the other, we observed corals losing their colour and turning an eerie ghostly white. Can corals recover from yet another episode of climate anomaly? Are we going to do anything differently, even if they do? Or will we allow the doomsday projections to come true and enter a world without coral by 2050? With measured hope, I will return to Nemo Reef each year looking for Acropora coral.