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Acidification in the oceans can cause hearing loss in small fish

Acidification in the oceans can cause hearing loss in small fish

As expected, the otoliths of the fish that were exposed to higher carbon dioxide levels were slightly larger — Radford was not surprised. “More importantly,” he adds, “the symmetry between the left and the right side was different.”

Symmetry is essential for animals on both sides, such as fish and humans. “If you look at someone’s face, most people are symmetrical, the left side matches the right side. It’s the same with all human sensory systems, “says Radford.” The brains of fish depend on symmetrical anatomy to calculate their perception. hearing from the raw sound. If you ignore this symmetry, the math in the mind changes and the fish’s hearing is less sensitive. “If you have otoliths that have a different shape,” says Radford, “then someone else will notice something different, which will make any form of sound localization more difficult.” If you lose your balance because water squeezes one ear, you have experienced something similar.

Radford’s team measured how ocean acidification can impair hearing. Radford placed tiny sensors on each modeled fish in the modeling clay, near the trunks of the brain. Then, when the fish returned to shape, the researchers struck tones and measured “auditory-induced potentials,” electrical signals received by the brain.

“We found that the low-frequency part of the hearing went down,” Radford says. At frequencies between 80 and 200 hertz, the hearing sensitivity dropped by about 10 decibels. Most vocal fish communicate at frequencies between 100 and 300 Hz, a deep murmur to build smooth ooo. And decibels run on a logarithmic scale: a decrease of 10 decibels means a ten times shrink. “It’s bad news, especially for fish, if they don’t hear it at those low frequencies,” Radford says.

Bignami is calmly embracing the results of the challenging models of the new study. Larger otolith should hearing has become more sensitive, as his model found, but the surprising contribution of the asymmetry between the left and right otoliths is more important. “It’s about measuring the actual neurological signals in young fish really it’s difficult, “he says of the new research.” It’s pretty compelling. They’re seeing a pretty clear change here. “

Otoliths overflowing with full effect on fish behavior, asymmetric anatomy and neurochemical effects. Ocean acidification is less taken by some fish brains with a neurotransmitter that controls impulsive behavior. (In an examination, larvae raised in acidified water swam in the direction the smell of predators.)

“We must not forget that he is studying a relationship that is really critical in life,” says marine researcher Sara Shen, who now works at an environmental consulting firm that has not been involved in the research. Shen’s previous research showed a link between the size of otoliths and the type of balance called vestibulo-ocular reflex at the sensitive transition point for fish larvae. The time chosen by Radford, where young fish settle on reefs, is very important to maintain populations. “It’s a really great job,” he says.

So what does this experiment tell us about how climate change affects reef fish? Ten percent of the hearing decreased by 120 percent increase in dissolved carbon dioxide among fish from 450 to 1,000 microsmospheres. CO2 it is a dissolved gas, the value of which represents the pressure it would otherwise have in an empty vessel, where one million microsmospheres is the normal air pressure. Such a large increase in average concentration will not occur in surface water in the coming years, although CO is adapting to long-term trends.2 emissions remain the same.

But even a smaller decrease in hearing acuity, caused by lighter acidification, would be significant. Young hearing fish can make an effort to find reefs as they migrate into the open ocean after hatching. If they cannot settle, they cannot survive and produce offspring. And these fish play an important role in maintaining the reefs. Predatory fish, for example, eat herbivores and, at the same time, keep algae growth under control. Mature algae break the coral. The coral dies and wears out. Fish shelters and egg-laying surfaces disappear along with this. “This ecosystem is disappearing,” says Yvonne Sadovy, a marine biologist at Hong Kong University who did not participate in the study.

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