Climate change will make the oceans more acidic and could damage sharks’ skin. Increased acidity corrodes the sharks’ denticles – microscopic tooth-like scales that cover their skin – which may impair their swimming.


The puffadder shyshark is at risk of ocean acidification
Juniors Bildarchiv GmbH/Alamy


As CO2 levels in the atmosphere rise further, the oceans will become more acidic, causing a bigger problem for sharks in the future, says Lutz Auerswald at the South African government’s Department of Agriculture, Forestry and Fisheries.

He and his colleagues decided to test the effects of differing aquatic CO2 levels on 80 puffadder shysharks (Haploblepharus edwardsii), a type of small cat shark that lives in shallow water, caught from a local harbour.

This species is already well-adapted to acidic waters, which are usually risky environments for aquatic animals because more CO2 can enter the blood, preventing oxygen from reaching the tissues. The puffadder shyshark gets around this problem by making its blood more alkaline, which can stop the sharks from getting associated health complications.

The team put the sharks into tanks with a pH of 8 – the current global level of oceans and seas – or a more acidic pH of 7.3 because they contain more CO2. After nine weeks in the more acidic conditions, the sharks could still employ the same tactics to keep their blood more alkaline but this came at the expense of their denticles.

This pH level, which is close to neutral, was enough to dissolve some of the mineral that makes up the scales. This is what makes the findings so surprising, says Auerswald – fizzy drinks, for example, typically have a pH of 3 or 4.

Although oceans aren’t predicted to drop to pH 7.3 until the year 2300, living near the western and southern coasts of South Africa makes the puffadder shyshark more susceptible to acidic waters than most. Climate change is likely to increase upwelling, a natural event that brings acidic water closer to the ocean surface where the sharks are found.

Shark teeth are made of the same material as their denticles, so this corrosion could also impair the shark’s feeding. Because denticles are found on all sharks, other species will probably be affected, says Auerswald. The great white shark, for instance, relies on its denticles for up to 12 per cent of its swimming speed. If they are worn away, these sharks might be unable to hunt as effectively and be more susceptible to injury while doing so.

Ocean acidification is a further pressure on sharks that already face the serious effects of overfishing, says Paul Cox at the Shark Trust, a UK conservation charity. “The compounding effects of pollution, deoxygenation, habitat destruction and ocean acidification will all place pressure on the 1200 or so species of sharks and rays in our ocean,” he says.