German scientists who exposed blacktip reef shark teeth to increasingly acidic water found the teeth developed cracks, holes, root corrosion and structural degradation — raising the possibility that ocean acidification driven by fossil fuel emissions could weaken sharks’ grip on their position at the top of the marine food chain. The researchers collected more than 600 discarded teeth from aquarium-held sharks and tested them against both today’s ocean acidity and the acidity projected for 2300. Their findings were published in the journal Frontiers in Marine Science.
The study adds ocean acidification to a list of mounting pressures on sharks — more than a third of whose species are already considered threatened with extinction — though outside scientists noted that overfishing remains the more immediate danger and that sharks’ evolutionary resilience may provide some buffer.
German scientists who tested the effects of ocean acidification on blacktip reef shark teeth found the teeth became structurally damaged under more acidic conditions — raising the possibility that rising ocean acidity driven by fossil fuel emissions could weaken sharks’ status as the ocean’s apex predator.
Researchers collected more than 600 discarded teeth from blacktip reef sharks housed at an aquarium, then exposed the specimens to water matching current ocean acidity and the acidity projected for the year 2300. Teeth exposed to the more acidic water developed cracks, holes, root corrosion and degradation to the tooth’s underlying structure, the scientists wrote. Their findings were published in the journal Frontiers in Marine Science.
“We found there is a corrosion effect on sharks’ teeth,” said Maximilian Baum, the study’s lead author and a marine biologist at Heinrich Heine University Düsseldorf. “Their whole ecological success in the ocean as the rulers of other populations could be in danger.”
A new hazard layered on existing threats
More than a third of shark species are currently threatened with extinction, according to the International Union for Conservation of Nature. The new findings identify ocean acidification as an additional hazard for animals that already face pollution, overfishing and broader climate change effects.
The ocean is expected to become almost 10 times more acidic than it currently is by 2300, Baum and his colleagues wrote. Acidification occurs when oceans absorb more carbon dioxide from the atmosphere, according to the National Oceanic and Atmospheric Administration. Scientists have linked the increase in atmospheric carbon dioxide to the burning of coal, oil and gas.
Sharks cycle through thousands of teeth in a lifetime, and those teeth are critical for regulating populations of fish and marine mammals, Baum said. Shark teeth are “highly developed weapons built for cutting flesh, not resisting ocean acid,” he said.
Outside scientists confirm the research, add context
Nick Whitney, a senior scientist at the Anderson Cabot Center for Ocean Life at the New England Aquarium, said the scientists’ work on shark teeth was sound. He noted, however, that because shark teeth develop inside the mouth tissue of sharks, they will be shielded from changes in ocean chemistry for a time.
Whitney also pointed to sharks’ long evolutionary track record. “They’ve been around for 400 million years and have evolved and adapted to all kinds of changing conditions,” he said.
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. He also cautioned that ocean acidification will pose broader challenges across the marine ecosystem — making it harder for shellfish such as oysters and clams to build shells, according to NOAA, and potentially weakening fish scales. Whether weaker prey could ultimately benefit sharks feeding on them remained unclear, Naylor said.
Baum said the acidification threat cannot be dismissed. Some shark species could come close to extinction in coming years, and ocean acidification could be among the factors causing that to happen, he said.
“The evolutionary success of sharks is dependent on their perfectly developed teeth,” Baum said.