How does rising atmospheric CO2 affect marine organisms?

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Corals and Fleshy Algae: Living Together in a Future World???
Smith, J.E., Price, N.N., Nelson, C.E. and Haas, A.F. 2013. Coupled changes in oxygen concentration and pH caused by metabolism of benthic coral reef organisms. Marine Biology 160: 2437-2447.

The authors write that "benthic marine primary producers affect the chemistry of their surrounding environment through metabolic processes." And they note, in this regard, that "photosynthesis and respiration will elevate or depress the concentration of oxygen in the diffusive boundary layer," while "acid-base regulation and biomineralization/dissolution for calcifying species can alter the relative concentration of inorganic carbon species and thus pH."

What was done
With the goal of comparing species-specific rates of change in pH and oxygen concentrations over a diel cycle for several species of common benthic coral reef organisms - including corals, turf algae, and fleshy and calcifying macroalgae - Smith et al. conducted similar studies in both the Caribbean and Pacific to assess the generality of results across divergent types of reefs.

What was learned
The four researchers determined that "more productive fleshy taxa have the potential to raise both oxygen and pH during the day to a greater extent than calcified species," which led them to state that their study, as well as the studies of Anthony et al. (2011) and Kleypas et al. (2011), thus suggest that "non-calcifying primary producers, especially those driving large amplitudes in diurnal pH fluctuations, may be important 'buffer organisms' against potential ocean acidification on coral reefs."

What it means
Simply put, Smith et al. conclude that "while particular species of macroalgae can negatively affect corals in a variety of ways," their study suggests that "some fleshy taxa may provide a buffering capacity to future ocean acidification scenarios," which suggests that sometime enemies can sometimes be friends.

Anthony, K.R.N., Kleypas, J.A. and Gattuso, J.P. 2011. Coral reefs modify their seawater carbon chemistry - implications for impacts of ocean acidification. Global Change Biology 17: 3655-3666.

Kleypas, J.A., Anthony, K.R.N. and Gattuso, J.P. 2011. Coral reefs modify their seawater carbon chemistry - case study from a barrier reef (Moorea, French Polynesia). Global Change Biology 17: 3667-3678.

Reviewed 11 December 2013