Baby sharks are being born smaller, undernourished and exhausted as climate change warms the world's oceans, researchers say.
Researchers examined the effects of warming temperatures on the growth, development and physiology of the Great Barrier Reef's epaulette sharks, testing embryos and hatchlings in waters up to 31 degrees Celsius (87.8 degrees Fahrenheit).
The research team found that in warmer waters, shark embryos grew faster and used their yolk sac -- their only source of food in this developmental stage -- quicker.
The creatures hatched earlier, were born smaller, and needed to feed straight away, but lacked energy, researchers from Australia's ARC Centre of Excellence for Coral Reef Studies at James Cook University and the University of Massachusetts said Tuesday.
There are more than 500 types of shark living around the world, and the majority give birth to live young. Some shark species, like epaulette sharks, lay eggs, which are left unprotected and must be able to survive on their own for up to four months.
"The epaulette shark is known for its resilience to change, even to ocean acidification," Jodie Rummer, co-author and associate professor at the ARC Centre of Excellence for Coral Reef Studies, said in a statement. "So, if this species can't cope with warming waters then how will other, less tolerant species fare?"
The Great Barrier Reef is the world's largest coral reef, covering nearly 133,000 square miles and is home to more than 1,500 species of fish, 411 species of hard corals and dozens of other species.
The past decade has been the warmest on record for global ocean temperatures. By the end of the century, the Great Barrier Reef is likely to experience average summer temperatures close to or exceeding 31 degrees Celsius, researchers warn.
Rummer said that rising ocean temperatures could threaten future sharks, including egg-laying and live-bearing species, because as temperatures rise, the creatures will be born or hatch into environments that they can barely tolerate.
"The study presents a worrying future given that sharks are already threatened," lead author Carolyn Wheeler said in a statement.
"Sharks are important predators that keep ocean ecosystems healthy. Without predators, whole ecosystems can collapse, which is why we need to keep studying and protecting these creatures," Wheeler, a PhD candidate at the ARC Centre of Excellence for Coral Reef Studies, added.
"Our future ecosystems depend (on) us taking urgent action to limit climate change," Rummer said.
The study was published in the Scientific Reports journal.
Oceans serve as a good indicator of the real impact of climate change -- covering almost three quarters of Earth's surface, they absorb the vast majority of the world's heat.
Although we often can't see it, ocean warming has a profound impact on the entire world. A warmer ocean causes sea level to rise, bringing problems like dangerous coastal flooding. It leads to the loss of sea ice, heating the waters even further, and can affect the jet stream, allowing cold Arctic air to reach farther south, making winters more intense and threatening animals that depend on sea ice.
A warmer ocean also contributes to increases in rainfall and leads to stronger and longer-lasting storms like Hurricanes Florence and Harvey.
Marine heatwaves which have killed off swathes of Earth's coral reefs have likely doubled in frequency and are projected to become more common and intense, a landmark report from the United Nations' Intergovernmental Panel on Climate Change found in 2019.