Some fish may be able to cope with rising CO2 in world’s oceans

London -  Researchers have revealed that some fish may be less vulnerable to high CO2 and an acidifying ocean than previously feared.

Investigators at the ARC Centre of Excellence for Coral Reef Studies (CoECRS) were behind these encouraging new findings.
 
“There has been a lot of concern around the world about recent findings that baby fish are highly vulnerable to small increases in acidity, as more CO2 released by human activities  dissolves into the oceans,” said Dr Gabi Miller of CoECRS and James Cook University.

“Our work with anemone fish shows that their babies, at least, can adjust to the changes we expect to occur in the oceans by 2100, provided their parents are also raised in more acidic  water,” Dr Miller noted.

Human activity is expected to increase the acidity of the world’s oceans by 0.3 to 0.4 pH by the end of this century, if the present trends in CO2 emissions continues, said co-researcher Prof  Philip Munday.

“Previous studies, and our own research, have shown that growth and survival of juvenile fish can be seriously affected when the baby fish are exposed to these sorts of CO2 and pH  levels,” he noted.

However when the researchers exposed both parents and their offspring in more acidic water they found that the anemone fish, at least, were able to compensate for the change.

“Whether this effect lasts all their lives, remains to be seen,” said Dr Miller.

How parent fish actually pass on this ability to deal with acidity to their offspring is still a mystery, said Prof Munday.

“The time interval is too short for it to be genetic adaptation in the normal sense. However, it’s an important parental effect that we need to factor in as we assess the vulnerability of the

world’s fish stocks to the planet-wide changes in ocean chemistry that humans are now causing,” he stated.

Based on evidence from past major extinction events, scientists have long feared that the acidity caused by the release of high levels of CO2 could cause havoc among sea-life, especially

those which depend on calcium to form their bones and shells. New research has also shown that higher CO2 levels can cause the nervous systems of some marine species to malfunction.

The recent increase in ocean acidity due to human activity in releasing carbon – about 0.1 of a pH unit over the last half century – is thought to be steeper even than in any of the past major

extinctions, which eliminated between 70-90 per cent of marine species.

“What this research shows is that some species, at least, may have more capacity to cope than we thought – which could help buy time for humanity to bring its CO2 emission under control,”

Prof Munday stated.

However Dr Miller cautions that anemone fish are particularly hardy by nature, and may not be typical of all fish in the ocean.

“They are definitely not the ‘canary in the coal mine’, as they have quite a large ability to cope with changed conditions anyway. We need to extend these studies to other types of fish,

especially those which humans rely on for food,” she suggested.

Both scientists warn that the major impact on ocean acidification is likely to be on the corals themselves, and the reefs which they form, which in turn provide the habitat for small fish such

as the anemone fish. The fate of the world’s reefs under a high human CO2 regime remains highly uncertain, they caution.

The study appeared in the online issue of the journal Nature Climate Change.