Scanning electron micrographs show that the denticles of puffadder shysharks kept in pH 7.3 water for nine weeks (right) were substantially more degraded than those of sharks kept in normal ocean water (left). J. Dziergwa et al/Scientific Reports 2019
Both groups of sharks adapted physiologically to the lower pH by pumping bicarbonate, a base, into their bloodstream to keep internal pH steady. In the sharks exposed for nine weeks, scanning electron microscope images of the sharks’ denticles revealed that, on average, 25 percent of denticles looked corroded, with duller edges and rougher surfaces. By comparison, 9.2 percent of denticles on three sharks kept nine weeks in normal ocean water were corroded. It takes longer than nine weeks for new denticles to form, Auerswald says, so the team can’t say whether chronic exposure impacts denticle development. The researchers did not look for denticle damage after acute exposure.
Valentina Di Santo, a marine biologist at Stockholm University who wasn’t involved in the study, was surprised to see this level of corrosion after just nine weeks. But “we should be careful not to generalize, because the sample size is very small,” she says. She’d like to see similar studies in other shark species, especially those that swim in open waters and whose survival is more dependent on speed.