Publisher : National Academy of Sciences
Place of publication :
Publication year : 2008
Thematic : Coral Reef
Language : English
Note
Ocean acidification represents a key threat to coral reefs by
reducing the calcification rate of framework builders. In addition,
acidification is likely to affect the relationship between corals and
their symbiotic dinoflagellates and the productivity of this association.
However, little is known about how acidification impacts on
the physiology of reef builders and how acidification interacts with
warming. Here, we report on an 8-week study that compared
bleaching, productivity, and calcification responses of crustose
coralline algae (CCA) and branching (Acropora) and massive
(Porites) coral species in response to acidification and warming.
Using a 30-tank experimental system, we manipulated CO2 levels
to simulate doubling and three- to fourfold increases [Intergovernmental
Panel on Climate Change (IPCC) projection categories IV
and VI] relative to present-day levels under cool and warm scenarios.
Results indicated that high CO2 is a bleaching agent for
corals and CCA under high irradiance, acting synergistically with
warming to lower thermal bleaching thresholds. We propose that
CO2 induces bleaching via its impact on photoprotective mechanisms
of the photosystems. Overall, acidification impacted more
strongly on bleaching and productivity than on calcification. Interestingly,
the intermediate, warm CO2 scenario led to a 30%
increase in productivity in Acropora, whereas high CO2 lead to zero
productivity in both corals. CCA were most sensitive to acidification,
with high CO2 leading to negative productivity and high rates
of net dissolution. Our findings suggest that sensitive reef-building
species such as CCA may be pushed beyond their thresholds for
growth and survival within the next few decades whereas corals
will show delayed and mixed responses.
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Keywords : Agathis kinabaluensis
Encoded by : Pauline Carmel Joy Eje
