Shark skin may get corroded by the acidifying oceans
When shark scientists handle sharks, they often come away with "shark burn."
"It will give you an abrasion," said Brendan Talwar, a research associate at the Cape Eleuthera Institute who studies sharks. "It's like sandpaper."
That's because shark skin is composed of hard scales, similar to microscopic teeth. But little to no research has been done on how the continually acidifying oceans — which absorb the skyrocketing carbon dioxide concentrations now amassing in the atmosphere — impact these scales, which, similar to your teeth, might corrode when exposed to carbonic acid (the result of adding carbon dioxide to water).
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Though it's just one novel study with a small number of sharks, new research published Thursday in the journal Scientific Reports found that shark scales on live puffadder shysharks were significantly corroded when exposed to nine weeks of acidified seawater.
"It's a bit far away from making conclusions for all sharks," said Lutz Auerswald, a biologist at Stellenbosch University in South Africa and an author of the research. But, he added, it's logical this scale corrosion could happen to other shark species. After all, acidified oceans eat away at the calcium shells in diverse marine critters.
"It makes sense because there’s calcium in the placoid scales of shark skin," said Bradley Wetherbee, a marine biologist at The University of Rhode Island who had no role in the research.
Some of Auerswald's co-researchers study the critically endangered great white sharks. But experimenting with these huge predators is obviously unrealistic, so instead, the research team chose freshly caught, 2-foot-long puffadder shysharks. "It’s not endangered, it’s small, and it’s easy to keep," Auerswald said.
The team exposed three sharks to normal seawater and three to more acidified ocean waters, similar to the natural acidity in certain parts of the ocean today, but a long, long way away from reaching average ocean acidity levels that might occur in the future (around the year 2300) — should civilization fail to rein in its colossal carbon emissions. Using a powerful microscope, the researchers found 25 percent of shark scales were damaged in the acidified water versus 9.2 percent damaged for sharks in the regular seawater.
This result demands more research, stressed Auerswald. After all, these scales play critical roles in the sharks' ability to swim efficiently and protect their bodies.
The globe's acidifying oceans won't immediately imperil any sharks. But it very well could be another burden on shark and ray species, 68 species of which are either endangered or critically endangered due to rampant overfishing, according to the International Union for Conservation of Nature. Overall, a quarter of shark and ray species are threatened with extinction.
"There are a lot of obstacles shark populations face," said Wetherbee. "The last thing they need is more negative effects that result from human impacts."
Already, research has shown acidified oceans could dull sharks' ability to sniff out food. This, combined with declining populations, incessantly warming seas, and now potentially corroded scales spell mounting strain.
"All these slights to their ability to function at the level they do now add up," said Cape Eleuthera's Talwar, who had no role in the research. "Then, [degraded skin] is a much bigger issue."
There's been a slew of research about how ocean acidification adversely impacts marine creatures like shellfish, as acidification has generally "decreased survival, calcification, growth, development, and abundance." But "this is a demonstration that we should be concerned about sharks as well," said Henry Bart, a fish researcher and director of the Tulane Biodiversity Research Institute.
"They’re a very vulnerable species to begin with," added Bart, who also had no role in the new research. "Climate change is just exacerbating that harm."
Unfortunately for life inhabiting the seas, ocean acidification will continually increase this century. "In recent decades, ocean acidification has been occurring 100 times faster than during natural events over the past 55 million years," notes the European Environmental Agency, a government entity. How much more acidic the oceans become this century is contingent upon the most uncertain part of the climate equation: how much carbon humanity decides to expel into the atmosphere.
It's not looking good. Carbon emissions are still going up, and may not even peak for a decade. Due to an unprecedented rate of carbon dioxide accumulation in the atmosphere, the seas are acidifying, rising, warming, and losing oxygen.
"It's only going in one direction quickly," said Rhode Island's Wetherbee. "You’re not expecting things to improve [in the ocean] unless something drastic happens."
What's more, there's growing evidence that as the climate warms, higher acidity conditions will become more frequent in certain regions of the oceans. This happens when deeper, more acidic waters well up from the deeper sea, exposing more fish to acidified conditions. In some regions off the South Africa coast, Auerswald notes profoundly high ocean acidity conditions (pH of 6.6) have been measured, much higher than even projections of how acidic the oceans might get by 2300 (pH of 7.3). "That's a pretty dramatic situation," he said.
There is good news, however, to come out of Auerswald's new research. The team also drew blood from 36 sharks that had been exposed to different levels of acidity. They found that internally, or physiologically, the sharks were able to withstand living in more acidic conditions. The sharks' blood work was OK.
But outside, on their degraded scales, it was clearly a different story.
"If they’re compromised by ocean acidification and a lower pH, that could be a concern for a lot of different species," said Wetherbee. "It could be another nail in the coffin for shark populations."
For now, sharks' greatest threat isn't ocean acidification. It's plummeting numbers, due to overfishing.
"None this will be anything to worry about in 2300 if we continue to harvest shark species at the rate we are now," said Talwar.
Topics Animals
Mark was the science editor at Mashable. After working as a ranger with the National Park Service, he started a reporting career after seeing the extraordinary value in educating people about the happenings on Earth, and beyond.
He's descended 2,500 feet into the ocean depths in search of the sixgill shark, ventured into the halls of top R&D laboratories, and interviewed some of the most fascinating scientists in the world.
