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Key predators are being forced from their homes by the climate catastrophe, endangering an ecosystem that is already struggling.

 "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," stated Dr. Anna Sturrock, a senior lecturer at the University of Essex who was not involved in the study team. Therefore, it is extremely concerning that sharks were leaving the reefs at the most vulnerable times. The good news is that not every shark acted in the same way.

Scientists have found that as the oceans continue to warm due to the climate catastrophe, sharks are leaving their habitats on coral reefs.

Sharks are already critically endangered, so this is likely to hurt them, and their disappearance could have detrimental effects on the already fragile reefs. The delicate and very diverse ecosystem that the reef sharks are a vital component of might get dangerously out of balance without them.

From 2013 to 2020, the researchers tagged and monitored around 120 grey reef sharks that were found on the isolated coral reefs of the Chagos archipelago in the central Indian Ocean. Sharks spent substantially less time on stressed reefs, especially during the strong El Niño event of 2015–16 that caused the ocean to warm. After a stressful occurrence, they were unable to return to their regular residence for up to 16 months.

In actuality, though, the sharks spent more time on a smaller percentage of the coral reefs. Due to the removal of invasive rats and increased numbers of birds that aid in fertilizing the reef, these reefs were healthier and more robust. Sharks may be able to stay on their home reefs if human-caused damage to coral reefs is reduced, according to the study. 

Because they have cold blood, sharks' body temperatures are correlated with those of the water. The project's leader, Dr. David Jacoby, a zoology lecturer at Lancaster University, stated that "if it gets too hot, they're going to need to move." It's alarming that a lot of people, in our opinion, are opting to go to offshore, colder, deeper waters. For extended periods, some sharks were completely absent from the reef.

Because of [overfishing], reef sharks are already endangered in around 20% of coral reefs worldwide. This new discovery could make the situation worse.

A quarter of all marine fish live in tropical coral reefs, which are remarkable and highly biodiverse ecosystems that are under threat from pollution, overfishing, and ocean warming. Even if the promises made in the Paris Climate Change Agreement come to pass, the great majority could disappear if global warming surpasses 2C, and the majority is expected to experience catastrophic bleaching episodes annually by the middle of the century. For food and a living, at least 500 million people depend on coral reefs.

The majority of the day is spent by the grey reef sharks under study on their home reefs, where they socialize, hunt reef fish, and seek refuge from larger open-water sharks. They graze primarily at night and off the reef. Upon their return, the other reef inhabitants benefit from their excrement.

More than 700,000 data points were collected during the study, which was published in the journal Communications Biology. Tags were employed to follow 120 sharks. In addition, nine distinct assessments of environmental stress on the reefs were obtained from satellite data, the most significant of which were sea surface temperature and patterns of wind and current.

Lead study author Dr. Michael Williamson, a post-doctoral research associate at the ZSL Institute of Zoology in London, stated that additional research was needed to confirm that the sharks were kept away by the heat's effect on the reef's health rather than by the heat driving them away right away.

"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," stated Dr. Anna Sturrock, a senior lecturer at the University of Essex who was not involved in the study team. Therefore, it is extremely concerning that sharks were leaving the reefs at the most vulnerable times. The good news is that not every shark acted in the same way.

Source theguardian.com