Rising human carbon dioxide emissions may be affecting the brains and
central nervous system of sea fishes with serious consequences for
their survival, an international scientific team has found.
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, says Professor Phillip Munday of the ARC
Centre of Excellence for Coral Reef Studies and James Cook University.
"For several years our team have been testing the performance of baby
coral fishes in sea water containing higher levels of dissolved CO2 –
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," Prof. Munday says.
In their latest paper, published in the journal Nature Climate Change,
Prof. Munday and colleagues report world-first evidence that high CO2
levels in sea water disrupts a key brain receptor in fish, causing
marked changes in their behaviour and sensory ability.
"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," Prof. Munday says.
Prof. Munday and his colleagues 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. But we suspected there was much more to it than the loss of
ability to smell."
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."
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