The world’s coral reefs could disappear within a few decades
along with hundreds of species of plankton and shellfish, according to new studies
into man’s impact on the oceans.
Researchers have found that carbon dioxide, the gas already blamed for causing
global warming, is also raising the acid levels in the sea. The shells of coral
and other marine life dissolve in acid. The process is happening so fast that
many such species, including coral, crabs, oysters and mussels, may become unable
to build and repair their shells and will die out, say the researchers.
“Increased carbon dioxide emissions are making the world’s oceans
more acidic and could cause a mass extinction of marine life similar to the
one that occurred on land when the dinosaurs disappeared,” said Professor
Ken Caldeira of the Carnegie Institution’s global ecology department.
When CO2 produced by burning fossil fuels dissolves in the ocean, it forms
carbonic acid. A little of this can benefit marine life by providing carbonate
ions — a vital constituent in the biochemical process by which sea creatures
such as corals and molluscs build their shells.
Caldeira found, however, that the huge volumes of carbon dioxide being released
by humans are dissolving into the oceans so fast that sea creatures can no longer
absorb it. Consequently, the levels of carbonic acid are rising and the oceans
are “turning sour”.
Speaking at the American Geophysical Union’s ocean sciences conference
in Hawaii last week, Caldeira said: “The current rate of carbon dioxide
input is nearly 50 times higher than normal. In less than 100 years, the pH
(measure of alkalinity) of the oceans could drop by as much as half a unit from
its natural 8.2 to about 7.7.”
This would mark a huge change in ocean chemistry. The shells of marine creatures
are made of calcium carbonate, the same substance as chalk, which is vulnerable
to acidity. Even a slight increase in acidity would mean many creatures would
dissolve. Others might be able to rebuild their shells but would be unable to
Nature, the scientific journal, recently published a study by Jim Orr, of the
Laboratory for Science of the Climate and Environment, Paris. It said that by
2050 the Southern Ocean and subarctic regions of the Pacific might be so acidic
that the shells of smaller marine creatures would start eroding.
Such a loss would have disastrous consequences for larger marine animals such
as salmon, mackerel, herring, cod and baleen whales. These all feed on pteropods,
or sea butterflies, one of the species most threatened by rising acidity.
Last week another warning was issued about the threat of acidity to sea life
at the annual meeting in St Louis of the American Association for the Advancement
Katherine Richardson, professor of biological oceanography at Aarhus University
in Denmark, said: “These marine creatures do humanity a great service
by absorbing half the carbon dioxide we create. If we wipe them out, that process
will stop. We are altering the entire chemistry of the oceans without any idea
of the consequences.”