By Joe Romm
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.
That’s
from an ARC news release on a new Nature
Climate Change study, “Near-future carbon dioxide levels
alter fish behaviour by interfering with
neurotransmitter function” (subs. req’d).
The
authors “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
known for quite some time about the threat global warming and human activity
poses to marine life (see Nature Geoscience study concludes ocean dead zones “devoid of fish and
seafood” are poised to expand and “remain for thousands of years“).
And we’ve known the threat ocean acidification poses
to shell-forming mollusks and crustaceans (see The Great Oyster Crash and Why Ocean Acidification Is
“A Ticking Time Bomb” for Both Marine Life and Humanity and links below).
Here’s
more on this ground-breaking new paper:
“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.
Catastrophic
global warming from unrestricted emissions of greenhouse gases remains the
gravest preventable threat to humanity, biodiversity and food security (see “Nature Publishes
My Piece on Dust-Bowlification and the Grave Threat
It Poses to Food Security“).
The time
to act was along time ago, but now is better than waiting until we have
irreversibly destroyed our ability to feed the 9 billion people we are
projected to have by midcentury.
Credit:
Image courtesy of ARC Centre of Excellence in Coral Reef Studies)