All Shark, No Bite – How Ocean Acidification Could Affect Shark Teeth

SHOW NOTES

Marine biologist and science journalist Max Baum is interested in how sharks are affected by major ocean changes – specifically, what more acidic oceans could mean for the sharks of tomorrow. But Max’s love for sharks goes beyond his specific research interests [11.01]. It began in childhood, where Max soon became known for his obsession with these enigmatic creatures: “I was the ‘shark kid’ in my class…in museums or aquariums, I was a little annoying kid explaining random things to other visitors. So I was always addicted to talk about sharks, explaining things about them.” This passion grew stronger over time, and accelerated during a family holiday to the Netherlands, where, aged 10, Max found his first fossil shark teeth. “I spent every summer after this sitting in the mud and in the tidal flats…searching for shark teeth all day,” he recalls.

Today, Max’s dual passions for shark science and sharing knowledge are reflected in his work as both a marine biologist and science communicator, bringing shark and marine science to wider audiences through his organisation Ocean Insights [13.16]. “I think the science communication is highly important today because what I already recognized through the media reports of my study, sharks are still highly negatively portrayed in media,” Max explains. “I very, very often cite the quote from Jaws: “you can yell barracuda, everybody says who, what? But you can yell shark, and we’ve got a panic on the 1st of July”.”

In this episode, Max is communicating the findings of his very own research, which investigated the potential effects of simulated ocean acidification on shark teeth [16.43]. A shark’s teeth don’t just look impressive; they are their most valuable asset, and a key reason for their perseverance throughout evolutionary time. Unlike humans, sharks can continuously replace their teeth throughout their lifetimes. Their dentition is also incredibly diverse across the different species – from serrated, knife-like teeth for slicing flesh to more plate-like teeth more designed for crushing shells, different species have evolved gnashers suited to just about every diet. “The diversity we have…is also something which plays a key role in the over 400 million years history of the ecological success of shark species,” says Max.

Ocean acidification is a chemical change, caused by an excess of carbon dioxide in the atmosphere [26.00]. “The CO₂  we release into the atmosphere as a greenhouse gas is not only making our planet warmer – about one quarter of it is absorbed or dissolves in the ocean,” Max explains. As a direct consequence, the pH of seawater is lowered, meaning it becomes more acidic. “The ocean today is 30% more acidic than 100 years ago,” says Max.

Ocean acidification is already known to affect organisms that rely on calcium carbonate, such as corals and shellfish. But sharks had received far less attention. “The question for our research was, what happens to calcified structures of larger animals like sharks – are shark teeth also affected?”

To investigate this question, Max and his collaborators turned to a previously untapped source of shark teeth: those naturally shed by blacktip reef sharks in his local aquarium [28.41]. It provided the perfect controlled setting in which to conduct his experiments. The team were able to gather hundreds of used teeth from a platform underneath where the sharks were fed on a daily basis, gaining a large sample without the need to harm live sharks or find funding for costly dive expeditions. Any teeth with cracks or breaks were discarded, leaving 60 teeth suitable for the experiment. These teeth were then placed in two tanks of water, which replicated two environmental scenarios: one with seawater of a ‘normal’ pH (8.1) and the other with a much lower pH (7.3). The latter represented a ‘worst-case’ future scenario for the year 2300. The teeth were submerged for eight weeks, after which time Max analysed them using electron microscopy.

Analysis showed that the teeth that had been exposed to the more acidic conditions showed signs of degradation [32.01]. “They looked darker. And we saw the ribbings on the root and also some cracks and holes in the crown,” Max recalls. To quantify these changes, Max developed something called the ‘corrosion per area index’, which used a kind of grid to measure the extent of the visible changes. “We saw that the acidified teeth have a lot more of corrosion, and also we found they have significantly more cracks and holes than the other ones.” It appeared that, in the span of just eight weeks, the structure of the blacktip teeth were becoming compromised.

But what does this mean for the sharks themselves [33.27]? It’s difficult to know for certain, as we are trying to predict something that is almost 280 years in the future. However, as we have already discussed, teeth are a shark’s most important tool. They are extremely specialised, so even small changes might have negative consequences on hunting success. It won’t be a dramatic impact by any means, but as Max says, ocean acidification must be considered alongside the many other pressures facing modern sharks: “Each stress factor is for itself maybe sometimes very small, but I really like to compare [it to] many needle stings sharks have to manage right now in our oceans. And I think what we found out is maybe one of 1000 needle stings.” From overfishing to pollution and climate change, sharks are dealing with multiple challenges at once — acidification could just add weight to an already heavy load.

Sharks do have a superpower up their sleeve; the ability to constantly replace teeth throughout their lifetime. Could this offer some resilience to the impact of ocean acidification [38.11]? It’s a question Max gets asked a lot. “Sharks can replace their teeth, yeah, but they also have to produce them,” he says, “and in more acidic water, we know that already from shells and corals, the production of calcium carbonate structures has a higher energy cost. Or other marine organisms, for example, some shells are producing thinner shells when the sea is more acidic. Maybe sharks will produce also some weaker teeth.” But with so many hypotheticals, it is extremely difficult to know for certain: “We don’t know. All just ideas and thoughts we are making right now…we need more data.”

Other studies suggest the effects of acidification may not be limited to teeth alone [42.40]. Similar corrosion effects have been observed on shark skin, which consists of tiny tooth-like denticles. Because these structures help reduce drag in the water, damage to them could impact swimming efficiency, causing sharks to require more energy to just keep moving.

Max is careful to emphasise that this research is just one step in our understanding; one study on one species in a controlled environment [47.39]. In his opinion, future studies could compare modern sharks with historical specimens or explore how slower-growing species respond over longer timeframes – like the world’s longest living vertebrate, the Greenland shark. But every insight is invaluable, and Max’s research highlights that this is one invisible threat that shouldn’t be ignored.

“I think one interesting thing to find out right now is where is the point where we can see these effects,” he muses, “because we tested the worst-case scenario in 280 years. Maybe we will be already able to see effects in 50, 80 or 100 years. We don’t know. Maybe we already have crossed this border because the oceans are 30% more acidic today than 100 years ago. So maybe we are already there.”

You can read the full paper discussed in this episode here.

ABOUT OUR GUEST

MAXIMILIAN BAUM

Max is a marine scientist and science communicator based in Germany, focusing on sharks and ocean changes. He combines hands-on research with storytelling to make marine science accessible to a wider public as a science journalist.

Instagram: MaxBaum_insights

LinkedIn: Maximilian Baum

https://ocean-insights.org/