Carnivorous crab preying on a Chilean sea snail (Concholepas concholepas).
Credit: Courtesy of Patricio Manríquez
Ocean Acidification Leaves Mollusks Naked and Confused
By Stephen Leahy
When the carbon dioxide absorbed by the oceans
dissolves in seawater, carbonic acid is formed and
calcium carbonate, vital for the formation of the
skeletons and shells of many marine organisms,
MONTEREY, United States, Oct 1 (Tierramérica).- Climate change will ruin Chilean sea snails'
ability to sniff out and avoid their archenemy, a
predatory crab, according to Chilean scientists
who presented their findings at an international
science symposium here.
Researchers from Australia also revealed that as
the oceans become more and more acidic, some fish
become hyperactive and confused, and move towards
their predators instead of trying to escape.
"The conditions in oceans are changing 100 times
faster than at any time in the past," said Jean-
Pierre Gattuso, a marine biologist with CNRS-INSU
and the Laboratoire d’Océanographie de
Villefranche in France.
Climate change is making oceans warmer and more
acidic. "We are beginning to understand what will
happen. I think we can expect the worst," Gattuso
Gattuso is one of nearly 600 scientists from
around the world who presented their research on
Sep. 24-27 at the Third International Symposium on
the Ocean in a High-CO2 World: Ocean
Researchers discovered only 10 years ago that
burning fossil fuels like coal, oil and gas has
made the oceans about 30 percent more acidic since
the beginning of the Industrial Revolution.
One third of the carbon dioxide (CO2) emitted from
using fossil fuels has been absorbed by the
oceans. When CO2 dissolves in seawater, carbonic
acid is formed. This phenomenon, known as ocean
acidification, reduces the availability of calcium
carbonate, which interferes with the formation of
the skeletons and shells of many marine organisms.
The combination of greater acidity and a lower
concentration of calcium carbonate in the water
also has consequences for the physiological
functions of numerous living beings.
This is basic, undisputed ocean chemistry. And
acidification will increase as more CO2 is
emitted, said the scientists meeting in Monterey.
Increasing acidity is affecting coral reefs,
shellfish and other shell-forming species, says
Pteropods, a very small free-swimming mollusk
species, are becoming "naked" because they are
losing their protective shell as acid levels
increase. Pteropods are food for many species and
a key element in the Southern Ocean and other
oceans, he said.
More surprising are the sub-lethal effects, such
as the recently documented changes in behavior.
In a sophisticated experiment, Chilean scientists
exposed Chilean sea snails (Concholepas
concholepas) to ocean acid levels expected before
the end of the century.
"It is called the 'Chilean abalone' in English and
is a very important food with high social and
economic importance in Chile," said researcher
Patricio Manríquez of the Institute of Marine
Sciences and Limnology at Austral University in
Its main predator is the Chilean intertidal
carnivorous crab (Acanthocyclus hassleri). The
snails can smell the crabs and move away to escape
Manríquez and colleagues built special tanks where
they could regulate the acidity of the seawater.
They collected snail larvae from north, central
and southern Chile and then reared them in labs
for five to six months under various high-acid
conditions, Manríquez told Tierramérica.
The researchers then put crabs in the tanks with
the snails to study their predator-prey
interactions under various levels of
At acidity levels expected when the amount of CO2
in the atmosphere rises from the current 390 parts
per million (ppm) to 750 ppm, the snails
immediately try to get as far away from the crabs
as they can.
At higher levels of 1,000 to 1,200 ppm CO2, the
snails seem confused and wander about aimlessly,
often going right towards the crabs.
“Good for the crabs, not so good for the snails,”
Those higher levels of CO2 could be reached by the
end of the century unless major emission
reductions are made.
"There was no change in the growth rates or size
of the snails," he said. However, at least 10
additional studies are underway regarding the
impact on the snails' shells, on snail larvae and
There are 10 scientists and 35 students from
different disciplines now investigating the
impacts of ocean acidification in Chile. However,
it still remains a challenge to have their
findings published in scientific journals, said
"Our methods and expertise are often questioned,"
he said, referring to the peer-review processes
carried out before research studies are published.
Manríquez maintains that this treatment for
Chilean academic studies goes far beyond
acceptable levels, and that he had not experienced
it when presenting work in collaboration with a
British research institute. .
Meanwhile, on the other side of the Pacific,
Australian researchers have learned that ocean
acidity affects behavior in some tropical reef
Ocean acidity acts to acidify the internal tissues
of fish and other water breathers, and while they
can deal with this, researchers have learned that
there are sub-lethal effects, said Philip Munday,
a researcher at the School of Marine and Tropical
Biology at James Cook University.
Ocean acidity levels expected after the year 2050
disrupt some coral fishes' central nervous
systems, altering their sense of smell, hearing,
vision and behavior, Munday told the Symposium.
"Their activity level, behavior and boldness
increase. They become more active and adopt more
risky behavior," he said. As a result, they are
twice as likely to be eaten by predators under
higher acid conditions.
Predators are affected as well. They are not as
efficient at catching their prey under these
conditions, for example. "Predators also switched
to different prey, which was something we did not
expect," he said. "It will be hard to predict all
of the impacts from higher ocean acidity."
Researchers here say that overfishing, including
bottom trawling, is the biggest immediate threat
to the oceans.
Ocean acidification and increasing ocean
temperatures are the big concerns in the years to
come. But those problems are more difficult and
will take longer to deal with, says Gattuso.
There is enough scientific evidence to advise
policymakers that action is needed now to reduce
CO2 emissions to protect the oceans for the
future, he said.