Experiments with sharks have shown that a decrease in the pH of seawater gradually destroys the hard “enamel” of their scales.
Cat shark scales: tomography / ©Rory Cooper, Kyle Martin, Amin Garbout, Natural History Museum London
The skin of sharks, like other cartilaginous fish, is covered with a special kind of scales — placoid. Anatomically, it is related not to wool, but to teeth, and individual scales consist of dentin with an enamel-like hard coating. This layer is sensitive to a decrease in pH, which is accompanied by global warming.
Additional carbon dioxide entering the atmosphere is partially absorbed by water, leading to its acidification. According to existing forecasts, by 2300 the pH of the World Ocean will fall below 7.3 (now it is about 8.1). A new article published in the journal Scientific Reports shows that this process poses a direct danger to the condition of shark scales.
Scientists led by Luntz Auerswald, professor at the South African University of Stellenbosch, used Haploblepharus edwardsii to study cat sharks. The fish were kept in water with a reduced pH value for nine weeks, after which the condition of their scales was checked. The outer layer of about a quarter of the scales was destroyed, whereas in the control group, less than 10% of the scales were damaged.
It is curious that in other aspects sharks were able to effectively resist acidification of water. Thus, blood samples taken from 36 fish that lived in water with a low pH showed that the increase in the intake of carbon dioxide into the blood is compensated by an increase in the content of carbonates in it. This allows sharks to consistently maintain optimal blood acidity. However, they cannot resist the long-term “corrosion” of the scales.
Scales play a big role in the life of sharks not only as protection. By stimulating the formation of microscopic turbulent vortices, the scales reduce water resistance when moving and allow the fish to swim much faster.