Shark teeth may weaken as oceans become more acidic

Sharks are built to catch moving prey with speed and precision. Their teeth do the heavy work, and new lab work suggests those teeth may not hold up as seawater becomes more acidic, according to a recent study.

Researchers tested naturally shed teeth from blacktip reef sharks under present day and projected future acidity. Teeth in more acidic water developed more surface damage after eight weeks.

Why shark teeth are important

The project was led by Maximilian Baum at Heinrich Heine University Düsseldorf (HHU). His team worked with discarded shark teeth collected from an aquarium in Germany to test how acidity affects their structure.

Sharks are elasmobranch fishes, a group that includes skates and rays, and they grow new teeth throughout life. Blacktip reef sharks even swim with mouths partially open to breathe, so their teeth are bathed in seawater all the time.

A shark tooth has a tough outer enameloid layer made of biological fluorapatite, with a softer dentin inside. This composition helps the crown stay sharp for cutting, while the root anchors the tooth to jaw tissue, and has porous osteodentin that is more exposed to chemical change.

Shark teeth in different water acidity

The team set up two tanks at pH 8.1 and pH 7.3 and incubated teeth for eight weeks. The lower value mirrors a long-term scenario used by climate assessments for the year 2300, as the ocean absorbs more carbon dioxide and pH declines.

Sixteen intact teeth were analyzed for corrosion patterns and surface changes. A larger set was imaged to track changes in measured circumference caused by roughening of serrations, not actual growth.

Impact of ocean acidity

Teeth at pH 7.3 showed more cracks and pits on the crown surface. They also showed more damage at the root where porous tissue is vulnerable.

Root corrosion covered about 8.2 percent of the root surface at pH 7.3, compared with 5.3 percent at pH 8.2, and those differences were statistically significant in the paper’s tests.

Surface roughening increased the measured circumference more in the low pH group, a sign of irregular edges that could weaken teeth under force.

Comparing with earlier studies

Previous research has found that certain sharks can keep tooth durability steady under moderate acidification. A 2022 study on Port Jackson sharks reported that teeth remained as durable under a pH drop of 0.3 units, linked to more fluoride in the tooth mineral.

The new test used a more extreme acidity and isolated, non living tissue, so it highlights chemistry alone. That design leaves out in body processes like remineralization or faster tooth replacement that living animals might use.

Physiology studies on young blacktip reef sharks show mixed effects when temperature and carbon dioxide rise together. One experiment found changes in blood measures and metabolism after short term exposure, with high individual variability that suggests energy costs could add up under stressful conditions.

Ocean acidity threatens shark teeth

Ocean acidification is driven by seawater uptake of carbon dioxide that forms carbonic acid and lowers pH. Foundational research shows that continued emissions can push pH declines over the next centuries, far beyond the small changes since preindustrial times.

The 7.3 scenario used in the tooth test is a worst case end member, but it helps reveal sensitivity in highly mineralized tissues.

If future acidity trends toward lower pH in coastal nurseries where young sharks live, cumulative exposure could matter over many tooth replacement cycles.

Weaker teeth and shark hunting

Sharper serrations can increase cutting efficiency in the short term. Roughened edges, however, can also create stress points where cracks start and spread, making a tooth more likely to chip during prey handling.

More frequent tooth replacement is a possible buffer, but that costs energy that sharks also need for growth, swimming, and reproduction. If tooth integrity drops while energy demands rise, hunting success could slip in ways that are hard to see at first.

“I think there will be effects on the teeth of ocean predators in general when they are highly mineralized structures like we have in sharks,” said Baum.

That view lines up with the lab images of cracks and holes across the transition from root to crown. Even small flaws in that zone can weaken the whole tooth under bite forces.

Future research directions

Live animal work can test whether sharks speed up tooth replacement or boost fluoride transport to harden new crowns under stress.

Those tests should measure mechanics directly, including toughness and fracture resistance, not just surface texture.

Field studies in reefs with natural carbon dioxide seeps could reveal whether wild teeth show similar microscale wear patterns. Coupling chemistry, mechanics, and behavior would show if damaged teeth actually reduce capture rates on real prey.

“Investigating adaptation mechanisms such as enhanced fluoride transport or ion regulation may reveal whether species like C. melanopterus can compensate for acidification effects, as suggested for other elasmobranchs,” wrote the researchers.

“Understanding these capacities is critical to assess future resilience and potential impacts on predator-prey dynamics and ecosystem stability.”

The study is published in the journal Frontiers in Marine Science.

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