The interplay between coral reef communities and seawater chemistry: Implications for the impacts of ocean acidification
Abstract
Researchers have known for some time that rates of photosynthesis/respiration and calcification/dissolution in shallow reef ecosystems can strongly control the seawater chemistry of the system. The past decade or so of ocean acidification research also shows the converse: that carbonate chemistry can affect the rates of calcification/dissolution, and to some extent photosynthesis/respiration. Coral reefs are considered vulnerable to ocean acidification, so understanding the interplay between seawater carbon chemistry and reef community functioning is important. For coral reefs that impose strong changes in their own seawater carbon chemistry, will ocean acidification still be a problem? Here, we report on two approaches toward quantifying the changes in the carbonate chemistry of seawater as it flows over shallow coral reef systems. Both approaches use a carbon flux model for photosynthesis, respiration, calcification and dissolution coupled with Lagrangian transport to examine how key groups of coral reef calcifiers (mainly corals) and primary producers (mainly macroalgae) contribute to changes in the seawater carbonate system as a function of water residence time. The first approach is based on carbon fluxes of corals and macroalgae from flume experiments, and shows that the drawdown of CO2 by macroalgae can ameliorate the effects of ocean acidification. Simulations for two CO2 scenarios (600 and 900 μatm) suggest that a potential shift from coral to algal abundance can lead to improved conditions for calcification in downstream habitats, depending on reef size, water residence time and circulation patterns. The second approach field tests the same model with data from a previous study of carbon fluxes along a reef-flat transect in Moorea (French Polynesia) (Gattuso et al. 1996). Both approaches show that, at least on shallow reefs, the upstream-downstream patterns of carbonate chemistry are affected by the spatial patterns of benthic community structure, and that increases in the ratio of photosynthesis to calcification can help compensate for ocean acidification. If the ratio of photosynthesis to calcification is not changed, however, ocean acidification depresses net calcification rates consistent with findings of previous studies.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMOS33B1671K
- Keywords:
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- 1615 GLOBAL CHANGE / Biogeochemical cycles;
- processes;
- and modeling;
- 4220 OCEANOGRAPHY: GENERAL / Coral reef systems;
- 4804 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL / Benthic processes;
- benthos;
- 4835 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL / Marine inorganic chemistry