Photo: David Clode//Unsplash
Sharks are leaving coral reef habitats as changes in the global climate influence ocean warming and bleaching, according to a new study published in the journal Communications Biology. The research was conducted on the remote coral reefs of the Chagos archipelago in the central Indian Ocean from 2013 to 2020, providing more than 700,00 data points from 120 grey reef sharks that had been tagged throughout that period.
The reef sharks researchers observed typically make reefs their daytime home where they find shelter from larger open-ocean predators. At nighttime, the grey reef shark heads out to feed and returns to its home reef again for the next day. Over time, and specifically during the El Niño winter of 2015-2016, researchers observed that the sharks spent more time away from their reef homes because of stressors like warmer ocean temperatures. They saw that in a major stress event like that El Niñ0 winter, the reef sharks didn’t return to normal residency for as much as 16 months.
“If it gets too hot, they’re going to need to move,” said Dr. David Jacoby, a lecturer in zoology at Lancaster University and the leader of the research project. “We think many are choosing to move into offshore, deeper and cooler waters, which is concerning. Some of the sharks were disappearing entirely from the reef for long periods of time. Reef sharks are already absent from nearly 20 percent of coral reefs globally, partly through [overfishing], and this new finding has the potential to exacerbate these trends.”
Naturally, the researchers believe that reef shark residency will only decrease as global ocean temperatures continue to climb. They pointed out that climate change is predicted to cause bleaching events annually by 2043, impacting the marine environments tremendously over that time period. Like anything else in a reef ecosystem, changes that can drive out or shift the behavior of one animal in the food chain can have a domino effect on the entire environment and all the species living there.
“Sharks play such an important role in keeping the reef system in balance, by eating both herbivorous and smaller predatory fish they help to keep coral from being overgrazed or overgrown by algae,” Dr. Anna Sturrock, a senior lecturer at the University of Essex, told The Guardian. “So it is very worrying that sharks were tending to leave during the reefs’ most vulnerable times. The hopeful side of it was that not all sharks did the same thing.”
