How Ocean Acidification Is Changing The Biology Of Sharks (and not for the better)

By Haley Davitz

The ocean is crucial to regulating the planet’s climate, as it absorbs about 25% of all carbon dioxide (CO₂) emissions. When there is too much CO₂ in the atmosphere, it traps heat, contributing to global warming. So, the ocean’s ability to absorb CO₂ is extremely important to keeping the global climate steady.

Since human activity has increased CO₂ emissions to exceptionally high levels, the ocean has been absorbing more and more carbon dioxide. The increase in CO₂ in the ocean causes the ocean’s average pH to decrease, meaning the ocean is becoming more acidic. This process is known as ocean acidification.

Ocean Acidification Impact On Sharks

Unfortunately, the increasingly acidic ocean is actually affecting the biology of sharks. Scientists have found evidence that ocean acidification is damaging sharks’ ability to track prey by odor and damaging their skin.

In one study, smooth dogfish (Mustelus canis) (Image 1) sharks, a relative of tiger sharks and bull sharks, were exposed to water with different CO₂, and consequently acidity, levels. The group of sharks in water with high CO₂ “significantly avoided odor cues” and less frequently “attacked” the food source compared to the control group, which was tested in water with today’s ocean acidity.

The high CO₂ level group was tested in water with predicted CO₂ level at the end of this century, if human emissions of CO₂ continue at the rate they are today. These findings indicate that the ability of sharks to properly respond to the odor of prey is damaged by increased CO₂ levels.

Another study examined the skin composition of sharks exposed to higher levels of CO₂. Groups of puffadder shysharks (Haploblepharus edwarsii) (Image 2) were exposed to high and low CO₂ environments and allowed to acclimate for one week. The group exposed to high levels of CO₂ showed damage to their denticles, or scales. After just one week of exposure, their denticles sustained corroded surfaces and dulled edges.

The Takeaway

If CO₂ emissions by human activity continue as they are, the ocean will become more and more acidic. By the end of the century, there will be so much CO₂ in the oceans that it will cause significant biological changes to sharks. Sharks will be less able to detect and track prey by following odor cues, and their skin will become damaged because of the acidity of the ocean.

Sources:
Dixson, D. L., A. R. Jennings, J. Atema, P. L. Munday.2015. Odor tracking in sharks is reduced under future ocean acidification conditions. Global Change Biology 21:1454-1462.
Dziergwa, J., S. Singh, C. R. Bridges, S. E. Kerwath, J. Enax, L. Auerswald. 2019. Acid-base adjustments and first evidence of denticle corrosion caused by ocean acidification conditions in a demersal shark species. Nature.com Scientific Reports 9:18668.

Image 1 from Barnegat Bay Partnership: https://www.barnegatbaypartnership.org/species/smooth-dogfish/
Image 2 Andy Murch