PORTLAND, Maine (AP) — Sharks are the ocean’s most fearsome predators, and their survival depends on fearsome teeth that regrow throughout their lives. But changes in ocean chemistry could put these weapons at risk.
That’s the conclusion of a study conducted by a team of German scientists that tested the effects of more acidic oceans on shark teeth. Scientists have linked human activities such as the burning of coal, oil and natural gas to the continued acidification of the oceans.
Scientists have found that as oceans become more acidic, sharks’ tooth structures may become weaker and more likely to break. This could change the position of large fish at the top of the marine food chain, they write.
The oceans won’t become filled with toothless sharks overnight, said the study’s lead author Maximilian Baum, a marine biologist at Heinrich Heine University in Düsseldorf. But Baum said the possibility of weakened teeth represents a new danger for sharks already facing pollution, overfishing, climate change and other threats.
“We found that shark teeth are corrosive,” Baum said. “As dominant species over other populations, their entire ecological success in the ocean could be at risk.”
Changes may happen gradually
The researchers, who published their findings in the journal Frontiers in Marine Science, conduct their study at a time when ocean acidification has become a growing focus for conservation scientists.
The National Oceanic and Atmospheric Administration says acidification occurs when the ocean absorbs more carbon dioxide from the air. German scientists write that by 2300, the ocean is expected to be nearly 10 times more acidic than it is today.
The scientists conducted their study by collecting more than 600 discarded teeth from aquariums housing blacktip reef sharks, a type of shark that lives in the Pacific and Indian oceans and typically grows to about 5.5 feet (1.7 meters) long. They then exposed the teeth to water with today’s acidity and an expected acidity of 2,300.
Teeth exposed to more acidic water suffer more severe damage, developing cracks and holes, root erosion and deterioration of the structure of the tooth itself, the scientists wrote.
The results “suggest that ocean acidification will have a significant impact on the morphological properties of teeth,” the scientists wrote.
Still the ocean’s apex predator
Shark teeth are “highly developed weapons for cutting meat, not for resisting ocean acids,” Baum said. Sharks replace thousands of teeth over their lifetimes, and these teeth are critical for sharks to regulate populations of fish and marine mammals in the ocean.
Many sharks are also at risk of extinction, with more than a third of shark species currently threatened with extinction, according to the International Union for Conservation of Nature. Thankfully, sharks have many factors that help them avoid the negative effects of ocean acidification, said Nick Whitney, senior scientist at the New England Aquarium’s Anderson Cabot Center for Marine Life.
Whitney, who was not involved in the study, said the scientists’ work on shark teeth is reasonable. However, because shark teeth develop within the shark’s oral tissue, they will be temporarily protected from changes in ocean chemistry, he said.
Whitney said history tells us that sharks are the survivors.
“They’ve been around for 400 million years and have evolved and adapted to a variety of changing conditions,” he said.
Gavin Naylor, director of the Florida Shark Research Program at the Florida Museum of Natural History, said ocean acidification may be a problem, but overfishing remains the biggest threat to sharks.
Acidification will bring about many changes
Naylor and others warn that ocean acidification does pose many threats to the ocean, not just sharks. The National Oceanic and Atmospheric Administration says ocean acidification is expected to be particularly harmful to shellfish such as oysters and clams because it will make it harder for them to build their shells.
It may also make the fish scales weaker and more brittle. Naylor said it’s hard to say now whether this will ultimately benefit the sharks that feed on them.
Currently, ocean acidification is a threat to sharks that cannot be ignored, Baum said. He said some shark species could be on the verge of extinction in the coming years, and ocean acidification could be one of the factors causing this.
“The evolutionary success of sharks depends on their perfectly developed teeth,” Baum said.
