PREVIEW

It’s not just humans who have to watch out for acidic drinks - as new evidence shows that the acidifying oceans are ruining sharks’ teeth.

The predatory fish may be able to replace their razor-sharp teeth throughout their lives – but even this remarkable ability might not be enough to protect them from climate change-related dental problems.

That’s because scientists in Germany have found that as oceans become more acidic, shark teeth grow weaker and more brittle, raising concerns for one of the seas’ top predators.

“Shark teeth, despite being composed of highly mineralised phosphates, are still vulnerable to corrosion under future ocean acidification scenarios,” said Maximilian Baum, a biologist at Heinrich Heine University Düsseldorf (HHU) and first author of the study published in Frontiers in Marine Science.

“They are highly developed weapons built for cutting flesh, not resisting ocean acid. Our results show just how vulnerable even nature’s sharpest weapons can be.”

Ocean acidification occurs when seawater absorbs human-produced carbon dioxide, lowering its pH and making it more acidic.

At present, the world’s oceans average a pH of 8.1. By the year 2300, researchers estimate this could fall to 7.3 – nearly ten times more acidic than today.

To test what this might mean for sharks, the researchers studied more than 600 discarded teeth collected from Blacktip reef sharks kept in an aquarium. Sixteen intact teeth were used in the experiment, while a further 36 were measured for changes in circumference.

The teeth were incubated for eight weeks in 20-litre tanks set to different acidity levels.

“This study began as a bachelor’s project and grew into a peer-reviewed publication. It’s a great example of the potential of student research,” said Prof Sebastian Fraune, senior author and head of the Zoology and Organismic Interactions Institute at HHU. “Curiosity and initiative can spark real scientific discovery.”

The results showed clear damage. Teeth exposed to more acidic water developed visible cracks, holes and root corrosion, alongside structural weakening.

“Tooth circumference was also greater at higher pH levels,” said Prof Fraune. “The teeth didn’t actually grow, but the surface structure became more irregular, so they appeared larger on 2D images.”

Although rougher teeth might cut more effectively, researchers warned they are also likely to be structurally weaker and more prone to breaking.

The study focused only on non-living mineralised tissue, meaning repair processes within living sharks were not considered.

“In living sharks, the situation may be more complex. They could potentially remineralise or replace damaged teeth faster, but the energy costs of this would be probably higher in acidified waters,” Prof Fraune said.

Blacktip reef sharks swim with their mouths permanently open in order to breathe, leaving their teeth continuously exposed to seawater.

“Even moderate drops in pH could affect more sensitive species with slow tooth replication cycles or have cumulative impacts over time,” Baum added. “Maintaining ocean pH near the current average of 8.1 could be critical for the physical integrity of predators’ tools.”

The researchers stressed that further work is needed to assess the impact on live sharks, including changes to tooth chemistry and resilience.

Nevertheless, they warned that even microscopic damage could pose a significant problem for predators that depend on their teeth for survival.

“It’s a reminder that climate change impacts cascade through entire food webs and ecosystems,” Baum concluded.