According to a new study, Grey Reef Sharks Abandon Coral Habitats, their homes as ocean temperatures rise. The study, conducted by marine experts at Lancaster University and the Zoological Society of London (ZSL) and published in Communications Biology, gives critical insights into how climate change is causing these Grey Reef Sharks to Abandon Coral Habitats.

From 2013 to 2020, the researchers observed grey reef shark movements using satellite remote sensing and a network of over 120 acoustic receivers put across coral atolls in the Indian Ocean. They collected over 714,000 acoustic detections and correlated them with satellite-measured environmental stress parameters.

“These findings provide some of the first evidence of how reef change in response to environmental stress, which is becoming more extreme and frequent, affects shark movement,” said principal investigator David Jacoby, a zoology lecturer at Lancaster University, in a news release.

High ocean temperatures, such as the 2015-2016 El Niño, have been related to coral bleaching, prompting sharks to leave their native reefs. This transition leads to more frequent and broad travels and extended absences from certain environments. Observations found that the altered behaviour remained for up to 16 months after such stressful events.

Grey reef sharks play an important part in preserving reef ecosystem balance. Their departure from reefs may upset this balance, endangering these ecosystems’ general health and resilience.

However, the sharks spent more time on a small percentage of the coral reefs. These reefs were healthier and more robust due to variables such as removing invasive rats and increasing bird populations, which aid in reef fertility. The researchers concluded that protecting coral reefs from human-caused damage may help sharks stay on their native reefs. Sharks are cold-blooded, and their body temperature is proportional to the water temperature. “If it gets too hot, they’re going to need to move,” said Dr David Jacoby. “We believe many are choosing to relocate to offshore, deeper, and cooler waters, which is worrying. Some sharks were missing completely from the reef for extended periods of time. Reef sharks have already disappeared from approximately 20% of coral reefs worldwide, owing to overfishing, and this discovery has the potential to aggravate these trends.”

“As large predators, grey reef sharks play a vital role in coral reef ecosystems,” explained lead author Michael Williamson, a postdoctoral research associate at ZSL’s Institute of Zoology. They maintain a delicately balanced food web on the reef and cycle nutrients onto coral reefs from deeper seas, where they frequently eat. The loss of sharks and the nutrients they carry could impact reef resilience during times of extreme environmental stress.

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