When sharks lose their bite

Climate change is causing the oceans to become notably more acidic. This could become a problem for sharks, as a team of biologists headed by Heinrich Heine University Düsseldorf (HHU) has discovered. In the scientific journal Frontiers in Marine Science, the research team describes that a more acidic environment weakens the teeth of sharks, causing them to break more easily, which in turn causes the predators to lose their bite.

As more of the greenhouse gas carbon dioxide (CO₂) is released into the atmosphere, more of this gas is also absorbed by the oceans. The consequence: The so-called pH-value of seawater decreases, making it more acidic. The acidity has a potentially corrosive effect on minerals – including those in the tooth material of marine organisms.

Sharks are known for being able to replace their teeth, with new ones growing to replace older ones when they wear down. This is crucial for their survival as they rely on their teeth to catch their prey.

A research team headed by Professor Dr Sebastian Fraune from the Institute of Zoology and Organismic Interactions at HHU has, in collaboration with biologists from the Sealife Oberhausen marine aquarium, examined the impact of ocean acidification on shark teeth. They placed shark teeth in containers of water at different levels of acidity: at the current pH of the oceans and at the expected pH in 2300.

“Shark teeth comprise highly mineralised phosphates, but they are susceptible to corrosion. The more acidic water in the simulated 2300 scenario damaged the shark teeth, including roots and crowns, much more than the water at the current acidity level. Global changes are thus so far-reaching that they can impact the microstructure of shark teeth,” says Maximilian Baum, former HHU student and now a freelance diver, photographer and speaker. He is the lead author of the study.

Corresponding author Professor Fraune: “The teeth are highly sophisticated weapons designed to cut flesh, but not to withstand the acidification of the oceans. Our results show how fragile even nature’s sharpest weapons can be. It is possible that the ability of sharks to replace their teeth on an ongoing basis will not be able to keep up with the changes in their environment.”

Teeth shed naturally by blacktip reef sharks (Carcharhinus melanopterus) kept at Sealife Oberhausen were used for the study. These teeth were divided between separate containers – one holding seawater with a pH of 8.1 (the current level) and the other with a pH of 7.3 (what is expected in 2300) – and incubated for eight weeks. Baum: “This pH corresponds to an almost tenfold increase in acidity compared with today.”

The teeth were then examined under the microscope at the Center for Advanced Imaging at HHU. Fraune: “At a pH-value of 7.3, we observed surface damage such as cracks and holes, increased root corrosion and structural deterioration. In addition, the surface morphology was more irregular, which can weaken the structure of the teeth and make them more susceptible to breaking.”

Timo Haussecker, Aquarium Curator at Sealife Oberhausen and co-author of the study: “As we only examined naturally shed teeth, the study does not take account of any repair processes, which may occur in living organisms. The situation may therefore be more complex in living sharks as they may be able to remineralise damaged teeth, albeit with greater energy expenditure.”

“Even moderate decreases in pH-values can impact more sensitive species with slow tooth replacement cycles or have a cumulative effect over the course of time,” adds Baum. “For sharks, it is certainly of great importance that the pH-value of the oceans remains near the current average of 8.1.”

Maximilian Baum and Professor Fraune conclude: “Our research reminds us that anthropogenic changes can impact entire food webs and ecosystems.”

Original publication

Baum M., Haussecker T., Walenciak O., Köhler S., Bridges CR. and  Fraune S.. Simulated ocean acidification affects shark tooth morphology. Front. Mar. Sci 12: 1597592 (2025).

DOI: 10.3389/fmars.2025.1597592