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For nearly 420 million years shark species have ranked among the world’s top predators. Most species are notorious for their fierce bite and incredible hunting ability. However, their status in the ocean could soon be under threat as deoxygenation of seawater is responsible for a rise in ocean acidity. More acidic waters corrode sharks’ skin and teeth affecting their ability to hunt, feed, and swim, according to a new study.
Published in the journal Scientific Reports, the researchers illustrate that exposure to acidified water over a prolonged period of time causes erosion of the denticles – the sharp scales that make up a sharks’ skin. While the study was conducted in the lab and focused on only the Puffadder shyshark (haploblepharus edwardsii), the implications of having more acidic oceans could be grave for all species of shark. In turn, this could also have a significant impact on the entire ocean food chain if certain species disappear.
“Some of the bigger species, like great white sharks, are also already highly endangered, so this might wipe them out,” stated Lutz Auerswald, the study’s senior author, fisheries biologist at Stellenbosch University in South Africa and the nation’s Department of Agriculture, Forestry, and Fisheries.
Interestingly, Auerswald and his colleague Sarika Singh, an ocean researcher at South Africa’s Department of Environmental Affairs, conceived of the study while casually talking over some beers outside of work. Acknowledging that the acidity of beer and other carbonated soft-drinks damages human teeth because the acid slowly dissolves the calcium and phosphate in the enamel, Singh pondered what effect the increase of acidity levels in seawater might have on sharks’ teeth and skin.
Deoxygenating Waters
Considering that today’s oceans are over 25% more acidic than the pre-industrial era, it can be said that human impact is threatening the condition of the planet’s oceans. The average pH level of today’s seawater is 8.1 compared with 8.2 prior to the industrial revolution. While this may seem an insignificant change, the relationship between pH and acidity is not direct. In fact, a decrease of 1 unit is a ten-fold increase in acidity. Severe acidification causes the shells, skeletons, and skin of marine life to dissolve.
This increase has also led to scientists and oceanographers declaring entire swathes of ocean ‘dead zones’, areas where oxygen levels are critically low, thus leading to depletions in marine life in these areas. On a greater scale, this effect on the marine ecosystem would also lead to socio-economic ramifications due to human dependency on marine life for food and goods services.
While the unstable chemistry of the ocean due to climate change has also been linked to coral bleaching over recent years, researchers were keen to address how this phenomenon affects specific species. This is what captivated Auerswald and Singh to pursue their curiosity concerning the effects of acidic waters on shark teeth and skin.
Into the Lab
Carrying out their experiments under laboratory conditions, Auserwald and Singh placed Puffadder Sharks in different aquariums that varied in pH levels while examining the effect of acid exposure on the skin using a high-resolution imaging technique. It took just nine weeks to determine that the water with high-acidity levels had damaged the denticles of the sharks' skin.
This kind of damage to the denticles can impair the way in which sharks swim and escape from perilous encounters.
In addition, since sharks’ teeth are from the same material, corrosion may impact hunting and feeding.
Lutz Auerswald, The study’s senior author and Fisheries Biologist, Stellenbosch University, South Africa and The Nation’s Department of Agriculture, Forestry, and Fisheries
All species of shark as well as other related fish such as rays, have skin and teeth made from that same material as the Puffadders, meaning they all could be vulnerable to increasingly acidic water.
The consequences, however, would likely “vary between species,” Auerswald says. Puffadder’s ambush their prey to feed, so damaged denticles might not impair their hunting ability. However, for larger species that hunt in open water, such as great white sharks, the denticles and skin play a vital role in hydrodynamics. According to one study, a shark’s denticles are responsible for up to a 12 percent increase in its swimming speed. Thus, corroded denticles could slow sharks down and make it increasingly difficult for them to be effective hunters.
Evolution and Climate Change
While sharks have continually adapted and met the challenges of environmental change – including deoxygenation and increases in ocean acidity – persistent and rapid changes in the pH of the ocean could eventually reach a tipping point. This is because sharks and their related species tend to have long generations, and this would make it more difficult for them to evolve in line with any extreme changes or events. What’s more, is that ocean acidification has also been linked to previous mass extinction events.
The rate of climate change is very fast compared to previous changes. Most likely, shark species will feel the impact differently and some may not be able to cope, whereas others may have the potential to adapt.
Lutz Auerswald, The study’s senior author and Fisheries Biologist, Stellenbosch University, South Africa and The Nation’s Department of Agriculture, Forestry, and Fisheries
Therefore, climate change and the current climate crisis is a very real threat to the oceans. If global climate trends continue at their current rate then many species – including humans – may find themselves suddenly threatened by any considerable changes in the marine ecosystem.
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