Global warming’s dark twin, ocean acidification, is
disrupting life in the oceans as dangerously as warming itself.
A recent study by University of Hawai`i researcher Nyssa
Silbiger and her colleagues indicates that coral reefs are eroding as
increasingly acid oceans eat away at their calcium carbonate structures.
(Image: MicroCT scan of experimental blocks reveals
bioerosion scars. Credit: N Silbiger, M Riccio/Cornell.)
Corals are always in dynamic tension, as the building work
of coral polyps is balanced against the destructive work of parrotfish and
boring marine worms. But studies at the University of Hawai`i Institute of
Marine Biology shows that acidification is tipping the scales toward
destruction.
The paper, Reefs shift from net accretion to net erosion along a natural environmental gradient,
by Silbiger, and co-researchers Òscar Guadayol, Florence I. M. Thomas and Megan
J. Donahuein, is in the journal Marine Ecology Progress Series.
Researchers placed coral blocks onto the Kane`ohe Bay reef
for a year, measuring them before and after by both weight and high-resolution computed
tomography (CT) scans. Different parts of the reef have different levels of
acidity, current flow, temperatures and other variables.
They found that the big predictor of coral erosion was
acidity of the water. And since oceans are expected to continue to acidify from
carbon-dioxide loading, that’s bad news for reefs.
And particularly bad news for reef areas subject to higher
levels of acidity. The study found that rather than being uniform, acidity
levels vary both in place and time.
“It was surprising to discover that small-scale changes in
the environment can influence ecosystem-level reef processes. We saw changes in pH on the order of meters
and those small pH changes drove the patterns in reef accretion-erosion,”
Silbiger said in a news release.
What does it all mean?
“Our findings suggest that increases in reef erosion,
combined with expected decreases in calcification, will accelerate the shift of
coral reefs to an erosion-dominated system in a high-CO2 world.
"This shift will
make reefs increasingly susceptible to storm damage and sea-level rise,
threatening the maintenance of the ecosystem services that coral reefs provide,”
the researchers write.
Citation: NJ Silbiger, O Guadoyal, FIM Thomas, MJ Donahue
(2014) Reefs shift from net accretion to net erosion along a natural
environmental gradient. Marine Ecology Progress Series, vol. 515, doi:
10.3354/meps10999
© Jan TenBruggencate 2014
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