Sharks’ survival may depend on more than just avoiding predators and finding prey as ocean conditions change, according to a study that examined how ocean acidification could affect sharks’ teeth.
In the study, a team of German scientists tested the effects of a more acidic ocean on sharks’ teeth and found that the teeth could become structurally weaker and more likely to break as acidity increases. The researchers published their work in the journal Frontiers in Marine Science.
Lead author Maximilian Baum, a marine biologist at Heinrich Heine University Düsseldorf, said the findings show a corrosion effect on sharks’ teeth. “We found there is a corrosion effect on sharks’ teeth,” Baum said, adding that the sharks’ “whole ecological success in the ocean as the rulers of other populations could be in danger.”
Baum said the ocean will not become populated with toothless sharks overnight, but weaker teeth would still represent “a new hazard” for sharks already facing multiple threats. He cited existing pressures including pollution, overfishing, climate change and others.
To conduct the experiment, the scientists collected more than 600 discarded teeth from an aquarium that houses blacktip reef sharks, a species found in the Pacific and Indian oceans. They exposed the teeth to two water conditions: acidity reflecting today’s ocean and projected acidity for the year 2300.
Teeth exposed to the more acidic water were “much more damaged,” the scientists wrote, with cracks and holes, root corrosion, and degradation to the structure of the tooth itself. The study also said the results show that “ocean acidification will have significant effects on the morphological properties of teeth.”
Ocean acidification is driven by the ocean absorbing more carbon dioxide from the air, the National Oceanic and Atmospheric Administration has said. The German scientists wrote that the ocean is expected to become almost 10 times more acidic than it is today by the year 2300.
Baum said shark teeth are “highly developed weapons built for cutting flesh, not resisting ocean acid.” He also said sharks go through thousands of teeth in a lifetime and that the teeth are critical for helping sharks regulate populations of fish and marine mammals in the oceans.
Nick Whitney, a senior scientist at the New England Aquarium who was not involved in the study, said the work was sound, but noted that shark teeth develop inside the sharks’ mouth tissue. He said that because of that, teeth will be shielded from changes in ocean chemistry for a time, and he pointed to sharks’ long history. “They’ve been around for 400 million years and have evolved and adapted to all kinds of changing conditions,” Whitney said.
Other conservation researchers cautioned that ocean acidification could harm more than sharks. Gavin Naylor, director of the Florida Program for Shark Research at the Florida Museum of Natural History, said overfishing remains the biggest threat to sharks, while acidification could also bring changes across the ocean ecosystem. Naylor said ocean acidification is expected to be especially harmful to shellfish such as oysters and clams because it would make it more difficult for them to build shells, as NOAA has said.
He also said acidification could make fish scales weaker and more brittle, and that it is tough to say now whether such changes could ultimately help sharks that feed on those species. Baum said for now ocean acidification cannot be disregarded as a threat facing sharks, and that some shark species could come close to extinction in the coming years, with acidification among the factors.
In his closing remarks, Baum said “The evolutionary success of sharks is dependent on their perfectly developed teeth.”