Ocean acidification may cause corrosion of shark skin

Future acidic ocean conditions could corrode the minerals in the strong scale-like skin of sharks, it could lead to reduce swimming capabilities and exposure to increased CO2 in their blood.

Sharks
Sharks are just the latest group of marine animals to be potentially affected by ocean acidification

As our oceans become increasingly warm as a result of climate change, they are also becoming increasingly acidic as an increased amount of atmospheric CO2 is absorbed at the surface. This ocean acidification is already having a serious effect of coral reefs and crustaceans, but new research has revealed another potential victim could be sharks. It has been shown that the super strong skin of these apex predators is susceptible to corrosion from acidic conditions, which can lead to some nasty consequences for those that are effected. Unfortunately it is just the latest in a long line of issues we are likely to see in the coming years as a result of acidifying oceans.

Teeth-like skin

If you have ever got up close to a shark then you would think from its initial appearance that it’s skin was seamlessly smooth, however if you were to reach out and touch it (not advisable unless you are with someone who knows what they’re doing) then you would be surprised to find it is rough and coarse like sand paper. That is because it is actually made up of thousands of tiny tooth-like structures called denticles. These ‘shark scales’ form an incredibly strong interlinking chain-mail armour that protect sharks from other sharks, as well as creating their speedy streamlined shapes.

Denticles
Overlaying denticles provide sharks with a streamlined and super-strong form of protective armour

Corroding like cola

The analogy between shark skin and teeth also runs much deeper than just appearance. That is because the denticles in shark skin are made up of dentine and other enamel-like minerals found in human teeth. If you have ever done the early school science experiment where you leave teeth in coca-cola or other fizzy drinks for a few days, then you will know the sugar and acidity quickly corrodes the teeth in a rather unpleasant way. This analogy is a much more extreme example of what acidic seawater could potentially do to the denticles in a shark’s skin. However until recently it was a very hypothetical issue with no real research done on how future acidic ocean conditions could corrode these minerals, and what the resulting effect on the sharks could be.

Testing in the lab

To answer this question a group of international researchers, lead by Jacqueline Dziergwa and based in South Africa, tested the effects on catsharks in laboratory conditions. They caught 80 puffadder shysharks (Haploblepharus edwardsii) from the local harbour for their experiment. They were chosen because they already have a high tolerance for acidic conditions, because they have adapted to have more alkaline blood to stop CO2 dissolving into it. They were placed into tanks with a pH of 8 (the current acidity of our oceans) and 7.3 (projected future conditions) for nine weeks, to compare any physiological changes brought about by increased acidity. Due to their alkaline blood the sharks were able to prevent dissolved CO2 from building up in their blood, however they did suffer some serious corrosion of their denticles with up to 25% of them sustaining permanent damage. The research team’s results were released in a paper published in December last year in the journal Nature.

Puffadder shyshark
A puffadder shyshark in its natural habitat in South Africa

Slower swimming & poisoned blood

The implications of corrosion to shark skin goes way deeper than just a dermatological nuisance, the loss of denticles can lead to multiple problems for these predatory animals. Firstly it can reduce their swimming speed. Sharks rely on their streamlined shape and overlaying denticles to allow them to move quickly through the water. For smaller species such as puffader shysharks this isn’t a major problem as they are predominantly bottom feeders, but for the true apex hunters like great white sharks, the level of damage from acidic oceans could mean the difference between them being able to make a kill or not. Additionally shark teeth are also made from the same material as their denticles and so if they were to sustain the same level of corrosion then their ability to feed would also be seriously compromised.

Great white
Great white sharks could be one of the shark species most severely affected

Whereas the puffadder shysharks are able to prevent CO2 from acidic seawater from entering their blood, thanks to their specially adapted alkaline blood, other species won’t be so lucky. As more CO2 enters the oceans, more of it will inevitably end up inside the blood and cells of marine creatures like sharks. The consequence of this will be that they are unable to absorb enough oxygen to maintain their vital functions like respiration. Experiments in fish have already shown that the results of this can be a debilitating form of intoxication known as hypercapnia. Whereas the sharks ability to swim and eat from day to day may be compromised as a result of denticle loss, acidification in the blood is something that could wipe out entire species in one go if they fail to adapt.

Acidic oceans

Since pre-industrial times the global acidity of oceans has increased by over 30%. This is already having an impact on calcium carbonate forming animals like corals and crustaceans, as well as anything else with a shell (and even some creatures without them). According to the latest estimates the average global pH of seawater won’t drop below the threshold of 7.3 until around 2300, so sharks are likely to be safe from corrosion for the foreseeable future. However unless something changes soon that change in acidity will become unavoidable and irreversible. Sharks are already facing extreme persecution from humans. They are misunderstood with regards to shark attacks and sensationalised media coverage, as well as being hunted in their millions for things like their fins and also meat. Even if they manage to survive for another 200+ years and survive the collapse of fish stocks and coral reefs, it seems they are likely to face a nasty and corrosive fate in our future acid oceans.


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