Blacktip reef shark. Credit: Stephen Frink / The Image Bank / Getty Images Plus.
Increasing ocean acidification is leading to unexpected impacts on marine life. A new study has found that it is causing more damage to shark teeth.
A leading cause of falling pH (lower pH means more acidity) in the world’s oceans is the absorption by the oceans of CO2 which is increasingly released into the atmosphere by the burning of fossil fuels.
The current average pH of Earth’s oceans is 8.1. This is projected to fall to 7.3 by the year 2300 – nearly 10 times more acidic than it is today.
Ocean acidification is already wreaking havoc on tiny creatures like diatoms and plankton which form the basis of the marine food web, and ecosystems such as coral reefs.
New research published in the journal Frontiers in Marine Science shows that ocean acidification is also affecting some of the seas’ top predators: sharks.
The findings are based on discarded teeth collected by marine scientists.
Sharks are known to replace their teeth. Their jaws house conveyer belt-like rows of sharp teeth which quickly come up to replace the ones lost in tussles with prey or rivals. A shark’s teeth are vital to the animal’s survival.
More than 600 discarded teeth from Blacktip reef sharks were collected from an aquarium.
A group of 16 intact and undamaged teeth were used as a control. A further 36 teeth were used to measure the change after 8 weeks in 20-litre tanks with pH values of 8.1 or 7.3.
“This study began as a bachelor’s project and grew into a peer-reviewed publication,” says senior author, Sebastian Fraune from the Heinrich Heine University (HHU) in Düsseldorf, Germany. “It’s a great example of the potential of student research.”
The teeth in the more acidic water suffered significantly greater damage.
“We observed visible surface damage such as cracks and holes, increased root corrosion, and structural degradation,” says Fraune.
The researchers also found the surface structure became more irregular. While such alterations could improve cutting efficiency, it potentially also makes teeth structurally weaker and more prone to break.
“Shark teeth, despite being composed of highly mineralised phosphates, are still vulnerable to corrosion under future ocean acidification scenarios,” says first author Maximilian Baum also from HHU. “They are high developed weapons built for cutting flesh, not resisting ocean acid. Our results show just how vulnerable even nature’s sharpest weapons can be.”
The research could not consider organic tissue in the teeth which might undergo repair processes in a living animal, reducing the damage.
“In living sharks, the situation may be more complex. They could potentially remineralise or replace damaged teeth faster, but the energy costs of this would be probably higher in acidified waters,” Fraune explains.
Blacktip reef sharks swim with their mouths permanently open to breathe, constantly exposing the teeth to water.
“Even moderate drops in pH could affect more sensitive species with slow tooth replication circles or have cumulative impacts over time,” Baum says. “Maintaining ocean pH near the current average of 8.1 could be critical for the physical integrity of predators’ tools.”
“It’s a reminder that climate change impacts cascade through entire food webs and ecosystems.”