NSF PR 97-19 - March 11, 1997
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First Evidence that Ozone Hole Harms Antarctic Fish
Researchers supported by the National Science Foundation
(NSF) have presented the first direct evidence that
increased ultraviolet light (UVB) damages the DNA
of animals in a natural population in Antarctica --
the eggs and larvae of icefish, an Antarctic fish
lacking hemoglobin. The ozone hole opens up over Antarctica
every southern spring, letting more UVB from the sun
penetrate to the earth's surface.
In an article published in the February 17 issue of
the Proceedings of the National Academy of Sciences,
biologists from Northeastern University and the University
of Texas demonstrated that icefish eggs accumulate
significant levels of DNA lesions called cyclobutane
pyrimidine dimers.
"We were surprised at the extent of the DNA damage
we found," said lead author Kirk Malloy, biologist
at Northeastern, "although we still need to know what
happens during the rest of the year when the ozone
hole closes up."
"Ozone depletion has previously been shown to harm
one-celled marine plants in Antarctica. We've now
documented significant damage at a higher level of
the food chain," said William Detrich, a Northeastern
biologist who coauthored the paper. "It is striking
how closely the damage to the fish eggs tracked with
the increased intensity of ultraviolet light."
The studies were done on cruises in waters around
the Antarctic Peninsula, the finger of land that juts
up toward South America.
The protective ozone layer over Antarctica has thinned
over the past two decades, as human-created chemicals
called chlorofluorocarbons have risen to the stratosphere
and helped to destroy ozone. Antarctica's ozone levels
typically drop to less than half of normal during
the spring ozone hole, allowing wavelengths of sunlight
harmful to life to penetrate to the earth's surface
and into ocean waters. The ozone layer has also thinned,
although less so, in temperate regions. Ozone depletion
is predicted across even broader areas of the globe
over the next century.
The excess ultraviolet light may slow a fish's growth,
hamper cellular processes such as transcription and
mitosis, and divert precious energy to DNA repair.
"Increased UVB may ultimately let fewer larvae survive
to adulthood," Malloy said.
The biologists also found that animals vary in how
fast they can repair damage to their DNA. Organisms
such as icefish and krill, which breed in spring and
release their eggs into ocean waters at the peak of
the ozone hole, can repair DNA more than twice as
fast as rockcod and other fish that breed in winter.
Detrich believes that animals that breed in spring
and summer when the sun is out "are a little better
prepared by nature to face the ozone hole."
The researchers' next step is to explore whether the
DNA damage actually does hamper the animals' ability
to survive. In any case, key members of the Southern
Ocean food web such as larval and adult fish, krill,
copepods, and some zooplankton -- the food base for
seabirds, whales, and seals -- could all be vulnerable
to increased UVB.
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