Sharks continually shed and regrow teeth throughout their lives, replacing worn or lost teeth with new ones. That makes them particularly good at catching prey. However, these top marine predators could lose their literal edge as ocean acidification damages their teeth and makes it harder to keep and replace them, a new study says.
“Shark teeth are highly evolved and diverse feeding tools developed over millions of years,” lead author Maximilian Baum, a biologist at Heinrich Heine University Düsseldorf, Germany, told Mongabay by email. “If their functionality is reduced due to acidification this could affect hunting success and energy balance and in the long run potentially impact survival and reproductive fitness.”
The world’s oceans are becoming more acidic as seawater absorbs the excess carbon dioxide (CO2) that humans pump into the atmosphere. This acidification disrupts the availability of calcium and other minerals in seawater, which harms organisms like corals and shellfish that use the minerals to form their shells and skeletons.
Shark teeth regeneration also depends on seawater minerals like calcium and phosphate. To find out how acidification might affect shark teeth, Baum’s team scuba-dived and collected naturally shed teeth from captive blacktip reef shark (Carcharhinus melanopterus), a critical predator in tropical coral reefs. “The sharks themselves were not an issue as blacktip reef sharks are very shy and peaceful,” Baum said. “The real difficulty was finding the small, shed teeth among sand and substrate and especially locating intact and freshly lost teeth that were suitable for the experiments.”
Studies project that as CO2 emissions continue to rise, the average pH of the ocean could drop from the current 8.1 to as low as 7.3 by 2300. So the researchers placed 26 undamaged teeth in water with pH 8.1, and 26 others in slightly more acidic water at pH 7.3.
At the end of eight weeks, the teeth exposed to more acidic water were significantly more damaged and weaker than the other group. “[W]e were surprised by how clearly the acidified teeth showed damage even after relatively short exposure times,” Baum said. “The difference in surface structure between the teeth from acidified and control conditions was obvious and consistent across our samples.”
While the experiment tested only shed teeth, Baum said they would expect to see similar damage in wild sharks as ocean acidification intensifies. This is because sharks swim with their mouths slightly open, so their teeth are constantly exposed to seawater.
In acidified seawater, the availability of minerals like calcium and phosphate necessary for new tooth formation may also be lower, Baum said, which could make the teeth regeneration process “even more difficult.”
“An increased need for new teeth combined with reduced mineral availability could create a biological bottleneck that affects shark performance and resilience,” he added. “Future studies on living animals are needed [if] we want to understand these dynamics better.”
Banner image: A blacktip reef shark by Charles J. Sharp via Wikimedia Commons (CC BY-SA 4.0).
