Recently, due to climate change and the increasing concentration of carbon dioxide in seawater, sharks, the 'top predators' of the ocean, are under threat. A new study has shown that ocean acidification weakens the hard teeth of sharks and increases wear. When teeth become weaker, sharks cannot hunt prey effectively, raising concerns that this could disrupt the entire marine food chain.
A research team from Heinrich Heine University in Germany announced on the 27th (local time) in the international journal 'Frontiers in Marine Science' that they confirmed that damage to shark teeth has become more pronounced as ocean acidification progresses.
Seawater is originally slightly alkaline, but when carbon dioxide (CO₂) in the atmosphere is absorbed by seawater, the hydrogen ion concentration (pH) decreases, leading to ocean acidification. Ocean acidification lowers the immunity and hinders the growth of marine organisms such as shellfish and corals. Before industrialization, the average pH of the world's oceans was 8.2, and it has now dropped to 8.1, indicating an increase in acidity of about 26%. It is expected to fall to 7.3 by 2300, which would be an environment roughly 10 times more acidic than now.
The research team selected intact teeth from over 600 discarded teeth of blacktip reef sharks for their experimentation. They immersed these teeth in water with pH levels of 8.1 (current) and 7.3 (acidified future) for eight weeks to compare the extent of damage.
The upper teeth of blacktip reef sharks have sharp structures with distinctive serrated edges. Observations using scanning electron microscopy (SEM) revealed that acidification corroded various structures of teeth such as the root, serrated edges, and crown. Teeth immersed in an environment of pH 7.3 exhibited more pronounced structural damage such as cracks, holes, and root corrosion. The surfaces became irregular, and the roots weakened, making them more prone to breaking.
In particular, blacktip reef sharks must swim with their mouths open to breathe, meaning their teeth are constantly exposed to seawater. If acidification worsens, the sharks' hunting tools will inevitably be damaged.
Previous studies have assessed that shark teeth are made of strong minerals, making them relatively resistant to acidic environments. However, the results of this study revealed that isolated shark teeth are vulnerable to damage such as cracks and corrosion, even in experimentally acidified conditions.
This study was conducted on already fallen teeth rather than living sharks, so the process of remineralization, where sharks make their damaged teeth strong again, was not reflected. However, the researchers noted that more energy would be consumed in this process under acidic conditions, potentially burdensome for shark survival.
The research team stated that future studies should directly analyze chemical changes and mechanical strength on the teeth of living sharks. Nonetheless, this study demonstrates that minor damage could be lethal for animals that hunt with their teeth.
Professor Sebastian Fraune, who led the study, said, "The corrosion of shark teeth can alter feeding efficiency and energy intake, ultimately leading to changes in the adaptability of soft-bodied fish like sharks," and added, "The impact of climate change will not stop at individual species but will spread throughout the entire food chain and ecosystem." He emphasized, "Maintaining the current average pH level of 8.1 is key to protecting the teeth, which are the survival weapons of sharks."
References
Frontiers in Marine Science (2025), DOI: https://doi.org/10.3389/fmars.2025.1597592