Damaged reefs turn butterflyfish into flexible eaters

Butterflyfish change their behaviour to adapt to coral death caused by climate change

Fewer options on the menu could force you to be a less fussy eater. At least that's what Lakshadweep’s melon butterflyfish experience, find scientists. In bleached coral reefs that host less food resources, these fish change their diets and eating patterns to adapt to reef damages caused by climate change.

Climate change–induced ocean warming can cause coral bleaching, which stresses coral patches and makes them prone to death. Bleaching is not new in Indian reef systems; the bleaching event of 2010 killed patches of corals in several reefs off the Lakshadweep Islands. This can be catastrophic for exclusive coral-eaters like melon butterflyfish. How do they deal with this?

Live coral cover

Scientists from Bengaluru's Nature Conservation Foundation (NCF) and National Centre for Biological Sciences (NCBS) studied live coral cover and butterflyfish numbers in three reefs fringing the islands of Kadmat (coral death was highest here with only about 7% live coral cover and, therefore, resource-poor), Bitra and Kavaratti (least coral death, nearly four times more live coral cover than Kadmat) in Lakshadweep. Surprisingly, their surveys show that despite these large differences in coral cover across the reefs, melon butterflyfish numbers were similar in all three.

Fish behaviour caught on the team’s underwater videos showed why. The video footage recorded the coral species that 58 pairs of melon butterflyfish they followed ate, the time the fish spent eating and the time they took to travel between patches of live coral to obtain food. In resource-poor reefs, fish ate coral species that they otherwise clearly avoided in rich reefs like Kavaratti. Fish spent more time travelling and less time searching for food in resource-poor reefs, making food procurement both difficult and energetically expensive. To compensate for this, the fish ate more ‘compulsively’ in such reefs, taking faster bites (about two times quicker than in rich reefs) off corals in a hurry, write the scientists in their study published in the journal Ethology.

This flexibility in butterflyfish is something that his team has documented in other reef fish such as predatory groupers too, wrote co-author of the study Rohan Arthur of NCF in an email to The Hindu. “What is emerging from reefs like the Lakshadweep is that the ability to be flexible is going to be a key ingredient that separates the ‘winners’ from the ‘losers’ as reefs decline,” he wrote. However, such short-term resilience may not guarantee longer-term survival, according to the scientists.