Study: Sharks feeding ability impaired by ocean acidification

A sand tiger shark. PHOTO COURTESY PAULA WHITFIELD, NOAA.
Some sharks may lose their edge as the world’s oceans become more acidic in the next few decades. Photo courtesy Paula Whitfield, NOAA.

‘In warmer water, sharks are hungrier but with increased CO2 they won’t be able to find their food’

Staff Report

The effects of ocean acidification on shellfish are already well understood. There’s little doubt shell-forming species like oysters will face big challenges as the water chemistry changes. In some cases, more acidic water will simply corrode there shells.

But a new study found that some top ocean predators will also be affected. Ocean acidification will impair the ability of some sharks to hunt and find food, according to researchers at the University of Adelaide (Australia).After assessing the results of some long-term experiments, the scientists concluded that ocean acidification will have major detrimental effects on sharks’ ability to meet their energy demands, with the effects likely to cascade through entire ecosystems. The findings have been published in the journal Scientific Reports.

The laboratory experiments, studying Port Jackson sharks and including large tanks with natural habitat and prey, found embryonic development was faster under elevated temperatures. But the combination of warmer water and high CO2 increased the sharks’ energy requirement, reduced metabolic efficiency and removed their ability to locate food through olfaction (smelling). These effects led to marked reductions in growth rates of sharks.

“In warmer water, sharks are hungrier but with increased CO2 they won’t be able to find their food,” said study leader Associate Professor Ivan Nagelkerken.

“With a reduced ability to hunt, sharks will no longer be able to exert the same top-down control over the marine food webs, which is essential for maintaining healthy ocean ecosystems,” Nagelkerken said.

PhD student Jennifer Pistevos, who carried out the study, explained that the Port Jackson shark is a bottom-feeder that primarily relies on its ability to smell to find food. Under higher CO2, the sharks took a much longer time to find their food, or didn’t even bother trying, resulting in considerably smaller sharks.

Most research studying the effects of ocean acidification and climate change on fish behaviour has concentrated on small fish prey. Long-term studies on the behaviour and physiology of large, long-lived predators are largely lacking.

University of Adelaide marine ecologist Professor Sean Connell said the results of the study provide strong support for the call to prevent global overfishing of sharks.

“One-third of shark and ray species are already threatened worldwide because of overfishing,” Connell said. “Climate change and ocean acidification are going to add another layer of stress and accelerate those extinction rates.”

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