Sharks are famous for their fearsome teeth. That could change

The fearsome teeth that define sharks as the ocean's apex predators, and are crucial for their survival, are now under threat from changing marine chemistry. A new study suggests that increasing ocean acidification could compromise these vital weapons.

German scientists conducted research into how a more acidic ocean environment affects sharks' teeth. Their findings highlight a direct link between human activities, such as the burning of fossil fuels, and the ongoing acidification of the world's oceans.

The study concluded that as oceans grow progressively more acidic, sharks' teeth risk becoming structurally weaker and more susceptible to breakage. This degradation, the researchers warned, could fundamentally alter the position of these powerful creatures at the pinnacle of the marine food chain.

The ocean will not become populated with toothless sharks overnight, said the study's lead author, Maximilian Baum, a marine biologist at Heinrich Heine University Düsseldorf. But the possibility of weaker teeth is a new hazard to sharks that already face pollution, overfishing, climate change and other threats, Baum said.

“We found there is a corrosion effect on sharks' teeth,” Baum said. “Their whole ecological success in the ocean as the rulers of other populations could be in danger.”

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The researchers, who published their work in the journal Frontiers in Marine Science, performed their study as ocean acidification has become an increasing focus of conservation scientists.

Acidification occurs when oceans absorb more carbon dioxide from the air, the National Oceanic and Atmospheric Administration has said. The ocean is expected to become almost 10 times more acidic than it currently is by the year 2300, the German scientists wrote.

The scientists performed their study by collecting more than 600 discarded teeth from an aquarium that houses blacktip reef sharks, a species of shark that lives in the Pacific and Indian oceans and typically grows to about 5.5 feet (1.7 meters) long. They then exposed the teeth to water with the acidity of today and the projected acidity of 2300.

The teeth exposed to the more acidic water became much more damaged, with cracks and holes, root corrosion and degradation to the structure of the tooth itself, the scientists wrote.

The results “show that ocean acidification will have significant effects on the morphological properties of teeth,” the scientists wrote.

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Shark teeth are “highly developed weapons built for cutting flesh, not resisting ocean acid,” Baum said. Sharks will go through thousands of teeth in a lifetime, and the teeth are critical for allowing sharks to regulate populations of fish and marine mammals in the oceans.

Many sharks are also facing extinction jeopardy, as more than a third of shark species are currently threatened with extinction according to the International Union for Conservation of Nature. Thankfully, sharks have a number of factors that can help them stave off the negative effects of ocean acidification, said Nick Whitney, senior scientist at the Anderson Cabot Center for Ocean Life at the New England Aquarium.

Whitney, who was not involved in the study, said the scientists' work on the shark teeth was sound. However, because shark teeth develop inside the mouth tissue of sharks, they will be shielded from changes in ocean chemistry for a time, he said.

And history has taught us that sharks are survivors, Whitney said.

“They've been around for 400 million years and have evolved and adapted to all kinds of changing conditions,” he said.

Ocean acidification could be a concern, but overfishing remains the biggest threat to sharks, said Gavin Naylor, director of the Florida Program for Shark Research at the Florida Museum of Natural History.

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Naylor and others cautioned that ocean acidification is indeed going to pose many threats to the ocean beyond just sharks. Ocean acidification is expected to be especially harmful to shellfish such as oysters and clams because it will make it more difficult for them to build shells, NOAA has said.

It could also make fish scales weaker and more brittle. It's tough to say now whether that could ultimately benefit the sharks that feed on them, Naylor said.

For now, ocean acidification can't be disregarded as a threat facing sharks, Baum said. Some shark species could come close to extinction in the coming years and ocean acidification could be one of the factors causing that to happen, he said.

“The evolutionary success of sharks is dependent on their perfectly developed teeth,” Baum said.