A close-up of Lakshadweep’s state animal, the melon butterflyfish (Chaetodon trifasciatus). Its distinctive yellow and white colouring with black stripes makes it one of the most recognizable fish on the reef.
While the world raves at the Great Barrier Reef, it’s easy to forget about the treasures found closer to home, in India. The Lakshadweep Islands, with their shimmering blue waters and vibrant marine life, are no less breathtaking. But beneath this beauty lies a fragile ecosystem, one that’s increasingly vulnerable to the blaring alarms of climate change and global warming which has only gotten worse over the last three decades.
Remember the recent El Niño event? No? Well, here’s what you need to know.
El Niño is a natural phenomenon that occurs every two to seven years on average, where due to a weakening of trade winds, the flow of warm water along the equator is reversed. The shift in oceanic current can heat the global oceans to as much as 1.6°C above the normal sea-surface temperatures, leading to a decline in rainfall and a subsequent increase in temperature in the Indian subcontinent. And while the heat might sound perfect for a beach day, it’s catastrophic for coral reefs.
A group of melon butterflyfish swim among branching corals in the pristine waters of Kavaratti. The abundant coral cover in healthy reefs provides both food and shelter for these specialized fish.
Coral reefs, often called the rainforests of the ocean, are built by tiny creatures called polyps that house colourful algae called zooxanthellae within their walls. Think of zooxanthellae as the reef’s personal chefs, they harness sunlight to produce oxygen and energy, which they share with their coral hosts. The by-products of photosynthesis comprise the majority of the coral’s food. In return, the corals provide the algae with shelter from the harsh ocean world. However, during El Niño events, the oceans grow so warm that as a stress response, the corals expel these algae, losing their vibrant colours in a process called bleaching. Without their algae partners, this framework of the reef often dies, jeopardising the entire ecosystem.
Coral reefs host a vast array of species. Among them, the butterflyfish (genus Chaetodon), takes the centre stage in a 2017 study led by scientists Amod Zambre, who was affiliated with the National Centre for Biological Sciences and Wildlife Conservation Society-India programme and Rohan Arthur from Nature Conservation Foundation. Butterflyfish are important bioindicators of a reef’s health, as they are sensitive to the changes in the surrounding environment. As obligate corallivores, these fish are picky eaters, dining exclusively on coral. Their survival hinges on the health of coral reefs. So, what happens to these specialists when coral disappears?
A researcher observes butterflyfish behavior (visible in background) while conducting underwater surveys in Lakshadweep. Notice how the fish stay close to coral formations while feeding.
To answer this, the researchers focused on three reefs in Lakshadweep after the 2010 El Niño event: Kadmat, Bitra, and Kavaratti. Each reef had experienced varying degrees of coral mortality – Kadmat had the highest mortality, Bitra was moderately affected, and Kavaratti remained largely pristine. Armed with snorkels, transect lines, and cameras, the researchers surveyed butterflyfish populations and behaviours, carefully cataloguing each detail. Picture them swimming a straight 50 meters in shallow waters, counting fish on either side, then repeating this feat dozens of times to build a reliable picture. All while they paid close attention to how these fish adapted to the changing availability of coral.
What they found was sobering to read. In Kadmat, where coral cover had been decimated, butterflyfish spent much of their day darting between coral patches in search of food. Travel times were long, energy demands high, and foraging bouts short, a stark contrast to the leisurely feeding routines where they could afford to be picky, spending up to 90% of their time foraging on their preferred coral in Kavaratti’s abundant reefs. Following the 2010 El Niño, despite their best efforts, the fish in Kadmat struggled to get enough nutrition with their total intake falling behind that of their counterparts in healthier reefs.
Butterflyfish feeding on healthy coral colonies in Lakshadweep. The white patches on the coral indicate early signs of bleaching, where stressed corals have begun expelling their symbiotic algae.
Yet, not all butterflyfish are created equal. Among the studied species, melon butterflyfish (Chaetodon trifasciatus) stood out for their resilience. Unlike other species like scrawled butterflyfish (Chaetodon meyeri) and redtail butterflyfish (Chaetodon collare) that saw their numbers drop in Kadmat, this one managed to persist, albeit with a twist. When faced with a shortage of their primary food source, these territorial and monogamous fish began including other coral species in their diet and were biting faster and more frequently. In fact, bite rates in Kadmat were three times higher than in Bitra and Kavaratti, a strategy that helped them partially compensate for reduced foraging time.
A solitary butterflyfish searches for food among degraded coral in Kadmat. The brownish, algae-covered substrate shows the aftermath of coral mortality, forcing fish to travel further between feeding sites.
This resilience, however, seems to come at a cost. In patchy reefs, these fish either tend to expand their territories, or turn to roving nomadically, abandoning the structured social behaviours seen in healthier reefs. In the long run, eating less nutritious corals and expending more energy to find them leaves little energy for reproduction potentially impacting the health of the entire population. Long-term studies elsewhere have shown that even seemingly resilient fish species can experience a lagging population crash years after the bleaching events.
It is a stark reminder that climate change is not a distant problem, it is unfolding here and now, in the reefs of Lakshadweep and beyond. Coral reefs are not just underwater wonders; they’re vital ecosystems supporting countless species, including humans who depend on them for food, coastal protection, and livelihoods. The Lakshadweep reefs may be small on the global map, but their importance is immeasurable.
References
Zambre, A. M., & Arthur, R. (2018). Foraging plasticity in obligate corallivorous Melon butterflyfish across three recently bleached reefs. Ethology, 124(5), 302-310. https://doi.org/10.1111/eth.12733
Pratchett, M. S., Wilson, S. K., & Baird, A. H. (2006). Declines in the abundance of Chaetodon butterflyfishes following extensive coral depletion. Journal Fish Biology, 69, 1269–1280. https://doi.org/10.1111/j.1095-8649.2006.01161.x
Pratchett, M. S., Wilson, S. K., Beruman, M. L., & McCormick, M. I. (2004). Sublethal effects of coral bleaching on an obligate coral feeding butterflyfish. Coral Reefs, 23, 352–356. https://doi.org/10.1007/s00338-004-0394-x
Graham, N. A. J., Wilson, S. K., Pratchett, M. S., Polunin, N. V. C., & Spalding,M. D. (2009). Coral mortality versus structural collapse as drivers of corallivorous butterflyfish decline. Biodiversity Conservation, 18, 3325–3336. https://doi.org/10.1007/s10531-009-9633-3