Acidifying Oceans Affect Sharks in Strange Way

A new study suggests that acidified ocean water produced by carbon emissions is causing sharks to swim much longer compared to when they swim in more typical less acidic water, especially during the night time. The findings of the study are particularly worrisome considering the effects of fossil fuel consumption by human beings will only serve to make ocean water more acidic. If the consumption of fossil fuels continues, sharks and other marine species are going to face even more challenges in the future, particularly when nearly 25 per cent of all shark species are already at risk of extinction.

“Usually when you expose a fish to some kind of environmental stressor, they acclimate to that stressor, and that makes them less vulnerable to that stressor, but here, it seemed like this high CO2 [carbon dioxide] continued to be a stressor to these sharks for quite a long time.” said study researcher Fredrik Jutfelt,

Acidifying Oceans

The earth’s ocean absorbs atmospheric carbon dioxide which decreases the pH level of ocean water and makes it more acidic. The National Oceanic and Atmospheric Administration says that on a 14 point scale, the pH of surface ocean water has declined by 0.1 since the start of the Industrial Revolution. What that effectively means is that surface ocean water has seen its acidity spike by as much as 30 per cent.

According to the results of a study of bony fish, a number of species have had a catastrophic reaction to the quickly acidifying oceans, whilst other species have seemed to be able to tolerate it. Dr. Jutfelt adds that hardly anyone had taken a close look at the effects of acidification on rays and sharks, which are species of marine life that are known for their cartilaginous bones.

Strange Swimming

The research team took 20 spotted cat sharks from an aquarium as part of their study. This species of shark is small but common throughout the Mediterranean Sea and Atlantic Ocean. Half of the sharks were placed in tanks containing typical ocean water with a pH of 8.1 and the other half were placed in acidified ocean water with a pH of 7.7.

After a four week period the researchers then examined the sharks to test for a variety of physiological responses such as oxygen consumption and blood pH levels. They also recorded the night time behaviour of the sharks when they are most active. What the researchers found was some odd night time behaviour exhibited by the sharks placed in acidic water.

“The control sharks, they would have these many starts and stops throughout the night. They would swim for a few seconds, or up to a minute, maybe, and then stop, but the CO2-exposed sharks, they kept swimming for longer time periods. Some of them swam for an hour continuously.” Dr. Jutfelt said.

Evolution Won’t Have A Chance To Work

The researchers thinks that the continuous swimming behaviour could be the product of changed ion concentrations in the brain of these sharks. Another explanation the researchers proposed was that the sharks were able to sense their water was too acidic and just continued swimming into order to reach water of a better quality which may be elsewhere.

The researchers say they do not know what this kind of behaviour would mean for sharks that live in the ocean, What they do know is that sharks take many years to reach sexual maturity and that means they reproduce slowly, so there will only be a few generations of sharks before the species is exposed to highly acidic water by 2100. That in turn means evolution will not have the chance to take its course and have a moderating effect which could be catastrophic for the species as a whole.