A pioneering study reveals that grey reef sharks are abandoning coral reefs during periods of environmental stress, such as high temperatures that cause coral bleaching. This behavioral shift holds significant implications for both shark populations and the balance of reef ecosystems.
Grey reef sharks, a vital component of coral reef ecosystems, are being forced to leave their homes due to increasing ocean temperatures, a new study finds.
The research, conducted by marine scientists at Lancaster University and the Zoological Society of London (ZSL) and published in the journal Communications Biology, provides urgent insights into how climate change is prompting these significant shifts in shark behavior.
Using a combination of satellite remote sensing and a network of over 120 acoustic receivers installed around coral atolls in the Indian Ocean, the researchers tracked the movements of grey reef sharks from 2013 to 2020.
They recorded more than 714,000 acoustic detections, correlating these data with satellite-observed environmental stress metrics.
“These results provide some of the first evidence of how reef change in response to environmental stress, something that is becoming both more extreme and more frequent, is affecting the movement of sharks,” principal investigator David Jacoby, a lecturer in zoology at Lancaster University, said in a news release.
High ocean temperatures, notably from events like the 2015-2016 El Niño, have been linked to coral bleaching, causing sharks to exhibit lower residency at their home reefs. This shift results in more frequent and widespread movements and longer periods of absence from these habitats. Observations revealed that the altered behavior persisted for up to 16 months following such stress periods.
Grey reef sharks play a crucial role in maintaining the balance within reef ecosystems. Their movement away from reefs can disrupt this balance, threatening the overall health and resilience of these ecosystems.
“As large predators, grey reef sharks play a very important role in coral reef ecosystems,” added 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 they also cycle nutrients onto coral reefs from deeper waters where they often feed. A loss of sharks, and the nutrients they bring, could affect the resilience of reefs during periods of high environmental stress.”