The epaulette shark relies on its unique characteristics to survive its taxing habitat in the Great Barrier Reef. Chief among them: its ability to walk.
The shark, which can also survive out of water for multiple hours, is built to survive the toughest ocean conditions. That’s why researchers are now looking to the creature, one of a handful of walking shark species, as an indicator of what climate change might bring in the decades ahead.
A study that examined how these sharks react to future climate scenarios, such as rising temperature, is raising concern for how other species – who may not be quite as well-equipped for climate change – might fare.
“Understanding how these animals do it and how they’re so successful, could teach us a lot about what is needed to be able to survive in the future climatic conditions that we’re supposed to see,” Marianne Porter, a biology professor Florida Atlantic University who works on a team that researches the early life development of the epaulette shark, told USA TODAY.
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What is an epaulette, a.k.a. the shark that can walk?
The slender, sandy-colored epaulette shark sports a large black spot on its side, resembling an epaulet, the shoulder piece worn on traditional military garbs, said Jodie Rummer, a marine biology professor at James Cook University in Australia who has studied the epaulette shark for more than a decade.
Multiple threats loom constantly over the epaulette shark. The shallow waters it inhabits warm significantly during the summertime during a low tide. But the small shark species must endure the harsh temperature – if it swims to deeper waters, it will be vulnerable to larger predators like bull sharks, Rummer said.
They use their ability to walk to hide inside the nooks and crannies of the reef to avoid being spotted and scooped up by aerial predators. They can even crawl over exposed coral reef and slide into another tide pool.
During the day, oxygen levels in its shallow habitat become dangerously high. In the nighttime, they become dangerously low. But the sharks withstand.
“These sharks don’t really have a reprieve,” Rummer told USA TODAY. “We talk about them as the toughest shark on the Great Barrier Reef. They don’t look so tough – not super bitey and super ferocious – but physiologically, they have got to be tough.”
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Shark’s response to simulated future climate conditions could spell danger for other species
Rummer, Porter and their team conducted research on sharks that published recently in the peer-reviewed Integrative and Comparative Biology science journal. Their research focused on the early life development of the shark.
They kept eggs in an environment that simulates what climate conditions could be like in the mid-to-late 21st century, Rummer said.
The researchers were alarmed by the impacts the simulated conditions had on the shark’s development.
They were much smaller. Their famous black spots began to discolor. They were hatching quicker. The yolk the hatchlings draw their energy from in the early stages of life depleted at an alarming rate, forcing the sharks to learn how to forage for food much earlier in life.
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If the toughest shark in the Great Barrier Reef responded so negatively to the ocean conditions of the future, then an even grimmer picture could be painted for the rest of the reef’s inhabitants, Rummer said.
“If we find these conditions are too stressful for this shark … That’s a really big warning system for the rest of the organisms on the reef, and definitely other shark species as well,” Rummer said.
Epaulette population changes could ‘upset the balance’
The fate of the reef’s ecosystem is also tied to the independent well-being of the epaulette shark, Rummer said. As a mesopredator, which both preys on smaller animals and is preyed upon by larger animals, the shark is crucial to maintain stability.
“If the numbers [of epaulette sharks] change at different times than the ecosystem is used to, that can really upset the balance,” Rummer said. “That affects the shallow reef habitats, which, of course, are connected to the deeper reef habitats, and then the open ocean as well… so thinking about it as all being very interconnected.”
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Now the researchers hope to learn more about what, if any, genetic adaptations the shark will make to survive under warmer conditions. But that takes generations, and in the case of these sharks, who reach sexual maturity at a late age and can live anywhere from 10 to 20 or more years, lots of time.
“What we really want is for this beautiful, quirky, walking shark that’s so tough, but not what you would expect,” Rummer said. “To be sort of that beacon for climate change education.”