Shark teeth are dissolving in more acidic oceans, scientists warn

Shark teeth are corroding under ocean acidification, threatening their survival and entire marine ecosystems. A new study warns future seas could weaken their most vital weapon.

The teeth of sharks are beginning to erode under the pressure of ocean acidification, one of the most direct consequences of climate change. A new study from Heinrich Heine University in Düsseldorf (Germany) shows that as seawater pH falls, the minerals that make up shark teeth corrode, threatening the survival of these predators and, by extension, the delicate balance of marine ecosystems.

A built-in dental plan, now at risk

Sharks are famous for their extraordinary ability to replace teeth throughout their lives. When one wears down or falls out, a new one simply grows in its place. This evolutionary trick has been essential for their survival, since their entire hunting strategy depends on a powerful, cutting bite.

But that natural advantage may not be enough to withstand the changing chemistry of the oceans. To test the impact of acidification, researchers placed shark teeth in tanks of seawater adjusted to different acidity levels: today’s average pH and the levels projected for the year 2300.

Oceans absorbing our emissions

As the atmosphere fills with carbon dioxide, the oceans absorb much of it. That extra CO₂ alters the chemistry of seawater, lowering its pH and making it more acidic. Based on current emission trends, scientists predict that the global ocean could drop from its present average of pH 8.1 to about pH 7.3 by 2300. It may sound like a small shift, but chemically it’s enormous.

“Shark teeth contain highly mineralized phosphates that are extremely sensitive to corrosion,” explained Maximilian Baum, the study’s lead author. “In the more acidic water scenario for 2300, we saw much greater damage to shark teeth, including both roots and crowns, compared to water with today’s acidity level. The global changes are so extensive that they can even affect the microstructure of shark teeth.”

Echoes of earlier warnings

This isn’t the first time marine biologists have sounded the alarm. Back in 2020, research led by the Southern California Coastal Water Research Project found that ocean acidification was already dissolving crab shells. The new shark study adds another worrying piece to the puzzle.

To carry out their experiment, scientists used naturally shed teeth from blacktip reef sharks (Carcharhinus melanopterus) kept at Sealife Oberhausen, a German aquarium. The teeth were divided into two tanks: one with seawater at today’s pH 8.1 and another at the predicted future pH 7.3. After eight weeks, the samples were analyzed under a microscope.

“At pH 7.3, we observed surface damage such as cracks and holes, more corrosion of the roots, and overall structural deterioration,” said Sebastian Fraune, who led the work. “In addition, the surface morphology became more irregular, which could weaken the teeth and make them more prone to breakage.”

A complex picture in living sharks

The scientists do caution that their study used shed teeth, not teeth still inside a living shark. This means it doesn’t capture the potential for biological repair processes. Sharks might be able to remineralize damaged teeth, though that would demand more energy—an extra burden in already stressed ecosystems.

“Even moderate decreases in pH can impact the most sensitive species, especially those with slower tooth replacement cycles, or have a cumulative effect over time,” Baum added. “For sharks, it is certainly crucial that ocean pH remains close to the current average of 8.1.”

The reminder is stark: human-driven change is reshaping entire food webs and ecosystems. And yet, as researchers note with some frustration, society too often acts as if it has forgotten this reality.

The study was published in Frontiers in Marine Science.

Sources: Heinrich Heine University / Frontiers in Marine Science