Carbon dioxide affecting fish brains

SYDNEY: Rising human carbon dioxide emissions may be affecting the brains and central nervous systems of sea fish, with serious consequences for their survival, according to research released Monday.

Carbon dioxide concentrations predicted to occur in the ocean by the end of this century will interfere with fishes' ability to hear, smell, turn and evade predators, the research found.

The Australian Research Council's Centre of Excellence for Coral Reef Studies said it had been testing the performance of baby coral fishes in sea water containing higher levels of dissolved CO2 for several years.

"And it is now pretty clear that they sustain significant disruption to their central nervous system, which is likely to impair their chances of survival," said Phillip Munday, a professor who reported the findings.

In a paper published in the journal Nature Climate Change, Munday and his colleagues also detail what they say is world-first evidence that high CO2 levels in sea water disrupts a key brain receptor in fish.

This causes marked changes in their behaviour and sensory abilities.

"We've found that elevated CO2 in the oceans can directly interfere with fish neurotransmitter functions, which poses a direct and previously unknown threat to sea life," said Munday.

The team began by studying how baby clown and damsel fishes performed alongside their predators in CO2-enriched water.

They found that while the predators were somewhat affected, the baby fish suffered much higher rates of attrition.

"Our early work showed that the sense of smell of baby fish was harmed by higher CO2 in the water, meaning they found it harder to locate a reef to settle on or detect the warning smell of a predator fish," said Munday.

The team then examined whether fishes' sense of hearing -- used to locate and home in on reefs at night, and avoid them during the day -- was affected.

"The answer is, yes it was. They were confused and no longer avoided reef sounds during the day. Being attracted to reefs during daylight would make them easy meat for predators."

The research also showed that the fish also tended to lose their natural instinct to turn left or right -- an important factor in schooling behaviour.

"All this led us to suspect it wasn't simply damage to their individual senses that was going on, but rather that higher levels of carbon dioxide were affecting their whole central nervous system."

Munday said around 2.3 billion tonnes of human CO2 emissions dissolve into the world's oceans every year, causing changes in the chemical environment of the water in which fish and other species live. (AFP)

Middle-Aged Brains Are Already Past Their Prime

You may want to read this twice if you're older than 45. In fact, you may have to.

That's because your mental abilities are already in decline, according to a study of 7,390 British civil servants just published in BMJ, the British Medical Journal.

For men and women who were between 45 and 49 when first tested, the ability to reason declined 3.6 percent over the next decade, the study found. And the decline was even faster for people in their 50s and 60s, especially men.

Other mental abilities that faded included memory, and so-called verbal fluency, which measures a person's ability to quickly say words in a particular category. However, people's vocabulary didn't change.

Previous studies have found little evidence of cognitive decline until people turn 60. But this study was larger than most earlier efforts and took the unusual step of testing each participant three times over 10 years.

 

The results suggest that efforts to head off mental problems late in life need to begin in middle age, the study's authors write at the end of their paper. These efforts should include "aggressive control" of problems such as diabetes, high cholesterol, and high blood pressure, which are linked to dementia and Alzheimer's disease, they say.

Perhaps, says epidemiologist Francine Grodstein of Brigham and Women's Hospital in Boston, who wrote an editorial accompanying the new study. The problem is that "we don't know yet how to prevent the small amounts of decline which begin to happen at younger ages," she says.

Even so, it may well turn out that the same things that affect memory at older ages also make a difference for younger people, Grodstein says. If so, "living a healthy lifestyle (e.g., a good diet, physical activity, etc.) starting at young ages might protect our brains when we're older," she says.

And even if you notice some lapses in memory as you age, there are likely to be other realms of thinking and decision-making where you improve. Barbara Strauch, author of The Secret Life of the Grown-up Brain: The Surprising Talents of the Middle-Aged Mind, says people's feeling of well-being is highest when they hit middle age. And some research indicates that older brains are better at solving problems than younger ones.

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