| Summary: | The effects of ocean acidification (OA) on coral reefs have been studied thoroughly with a focus on the response of calcification of corals and calcified algae. However, there are still large gaps in our knowledge of the effects of OA on photosynthesis and respiration of these organisms. Comparisons among species and determination of the functional relationships between pCO2 and either photosynthesis or respiration are difficult using previously published data, because experimental conditions typically vary widely between studies. Here, we tested the response of net photosynthesis, gross photosynthesis, dark respiration, and light-enhanced dark respiration (LEDR) of eight coral taxa and seven calcified alga taxa to six different pCO2 levels (from 280 to 2000 ??atm). Organisms were maintained during 7???10 days incubations in identical conditions of light, temperature, and pCO2 to facilitate comparisons among species. Net photosynthesis was not affected by pCO2 in seven of eight corals or any of the algae; gross photosynthesis did not respond to pCO2 in six coral taxa and six algal taxa; dark respiration also was unaffected by pCO2 in six coral and six algae; and LEDR did not respond to pCO2 in any of the tested species. Overall, our results show that pCO2 levels up to 2000 ??atm likely will not fertilize photosynthesis or modify respiration rates of most of the main calcifiers on the back reef of Moorea, French Polynesia.
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