A study published in the journal Frontiers in Marine Science has challenged the invulnerability of shark teeth. The research, led by Maximilan Baum from the University of Düsseldorf, highlights a threat: the increasing acidification of the oceans. Specifically, when subjecting teeth from the blacktip reef shark (Carcharhinus melanopterus) to extreme pH conditions (7.3, projected for the year 2300), scientists observed significant corrosion. This chemical process weakens the mineralized structure of the teeth, increasing fragility and the risk of fracture—a risk that Baum illustratively compares to “the effects of drinking a cola” on human enamel. This situation threatens the survival of marine ecosystems, especially that of sharks, which rely entirely on their dental health to feed and survive.
Eternal dentition
Can you imagine not having to worry if you lose a tooth (that isn’t a baby tooth), because in just a matter of days you would have another fully functional one without needing to visit the dentist? Well, this is exactly what happens in a shark’s mouth. Over almost 400 million years, evolution has perfected this system into a biological conveyor belt of teeth. This system allows species like the lemon shark (Negaprion brevirostris) to replace more than 30,000 teeth throughout their lifetime.
Each tooth is attached to the jaw not by rigid gums as in humans, but by connective tissue with rows of teeth folded backward. When a tooth is lost in combat or during hunting, a reserve tooth can take its place. Their teeth have an outer layer of highly mineralized enamel and a dentin base, making them exceptionally hard. However, its own architecture, which allows for constant renewal, hides a vulnerability that is being exploited by the chemical change of the oceans.
Ocean Acidification
The main threat to sharks’ teeth is not biological, but chemical. The increase in carbon dioxide (CO2) emissions in the atmosphere is absorbed by the oceans, a process that lowers the water’s pH, making it more acidic. This ocean acidification directly affects sharks’ teeth, which are rich in calcium and phosphate minerals. These compounds are stable in the normal alkaline pH of seawater. However, as the pH decreases, the environment becomes corrosive to these structures.
Düsseldorf Experiment
The research published in Frontiers in Marine Science focused on exposing naturally shed teeth of Carcharhinus melanopterus to extreme acidity conditions expected in the future. The pH 7.3 environment simulated an exaggerated but plausible scenario for the year 2300. Maximilan Baum’s team documented that acidic immersion caused undeniable physical damage, including:
- Increase in corrosion.
- The appearance of structural cracks.
- General weakening of the dental crowns.
The results isolated the “purely chemical effects of ocean acidification on non-living mineralized tissue”, demonstrating that the tissue itself is vulnerable to dissolution. Unlike mammals, whose tooth roots are anchored and protected within the gums, shark tooth roots are “directly exposed to seawater”. This constant exposure subjects them to direct exposure and attack without any protection. The study warns that ecological impacts could manifest much earlier than the most extreme predictions. Even moderate reductions in pH combined with other factors such as overfishing, reduced food availability, or pollution could decimate the shark population.