SYDNEY Climate change might be causing reef
fish to get lost, unable to return to breeding grounds from the
open ocean, which could have profound implications for the
survival of reef ecosystems, Australian scientists say.
Climate change-induced environmental stress, including
warmer and more acidic seawater, could be hindering the
development of the ear bones in young reef fish, which rely on
sound for navigation, the marine experts said on Friday.
The scientists from the James Cook University and the
Australian Institute of Marine Science found that fish with
asymmetrical ear bones struggle to return to their home reef.
"In our opinion, ear bone asymmetry in the early life
stages of reef fish interferes with their capacity to find and
settle on coral reefs," fish ecologist Monica Gagliano said in
Fish at the end of their "ocean stage" after hatching
navigate by homing-in on reef-associated sounds, such as the
gurgling of fish and the snapping of crustaceans, said the
scientists, whose study was published on Friday in the British
scientific journal Proceedings of the Royal Society.
Vertebrate animals make sense of sounds by comparing
differences in the acoustic signal between their two ears. To
do this well, ear structures must be relatively symmetrical.
Asymmetrical ear bones do not appear to make the fish deaf, but
might interfere with the ability of the fish to hear
The scientists said ear bone asymmetry could be closely
linked to rising sea surface temperature and acidity, caused by
high atmospheric carbon dioxide levels, as well as localized
stresses. Oceans absorb CO2 from the atmosphere, acting as a
giant sink for the greenhouse gas.
Fish ear bones, like fish skeletons and reef-building
corals, are made from calcium carbonate. When seawater becomes
more acidic, there is less calcium carbonate available for
building calcium-based structures, including fish ear bones.
LOST AT SEA
The scientists studied damselfish, which are abundant on
Australia's Great Barrier Reef and western Australia's Ningaloo
Reef, and found that at hatching, 41 percent of a sample group
of fish had symmetrical ear bones and 59 percent asymmetrical.
When the scientists examined the ear bones of fish
returning from open ocean to settle on the reef a few weeks
later, far fewer asymmetrical fish made their way back to the
The scientists also found that those with asymmetrical ear
bones that did make it to the reef took longer to do so than
their symmetrical counterparts.
"There is a degree of asymmetry that is acceptable in the
population, some is natural," said scientist Martial
"Not all the babies are created equal and not all of them
are going to make it, even in pristine environments," said
But Depczynski said the already high mortality rate among
reef fish hatchlings was likely to rise even higher if young
fish could not navigate by sound.
The scientists said they suspected asymmetrical ear
development might be responsible for a drop in the number of
damselfish in recent years, but more study was needed.
"Five years ago we used to see them in the thousands, now
they are not so plentiful," said Gagliano.
(Editing by David Fogarty)