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| Rising levels of carbon dioxide is affecting fish nervous system and brain |
ScienceDaily, January 20, 2012
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 Philip 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."
Other work showed
the fish also tended to lose their natural instinct to turn left or right -- an
important factor in schooling behaviour which also makes them more vulnerable,
as lone fish are easily eaten by predators.
"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."
The team's latest
research shows that high CO2 directly stimulates a receptor in the
fish brain called GABA-A, leading to a reversal in its normal function and
over-excitement of certain nerve signals.
While most animals
with brains have GABA-A receptors, the team considers the effects of elevated
CO2 are likely to be most felt by those living in water, as they
have lower blood CO2 levels normally. The main impact is likely to
be felt by some crustaceans and by most fishes, especially those which use a
lot of oxygen.
Prof. Munday said
that 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.
"We've now
established it isn't simply the acidification of the oceans that is causing
disruption -- as is the case with shellfish and plankton with chalky skeletons
-- but the actual dissolved CO2 itself is damaging the fishes'
nervous systems."
The
work shows that fish with high oxygen consumption are likely to be most
affected, suggesting the effects of high CO2 may impair some species
worse than others -- possibly including important species targeted by the
world's fishing industries.
Story Source:
The above story is reprinted from materials provided by ARC Centre of Excellence in Coral Reef Studies.Note: Materials may be edited for content and length. For further information, please contact the source cited above.
Journal Reference:
- Göran E. Nilsson, Danielle L. Dixson, Paolo Domenici, Mark I. McCormick, Christina Sørensen, Sue-Ann Watson, Philip L. Munday. Near-future carbon dioxide levels alter fish behaviour by interfering with neurotransmitter function. Nature Climate Change, 2012; DOI:10.1038/nclimate1352
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