How does rising atmospheric CO2 affect marine organisms?

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Inshore Turbid Reefs of Australia: How Resilient Are They?
Browne, N.K. 2012. Spatial and temporal variations in coral growth on an inshore turbid reef subjected to multiple disturbances. Marine Environmental Research 77: 71-83.

The authors write that "turbid reefs are typically situated in shallow waters within close proximity to the coast, where high sediment yields and wave-driven resuspension of fine sediments on the seafloor lead to large fluctuations in turbidity [that] reduce water transparency and limit light availability for phototrophic organisms (Loya, 1976; Anthony and Connolly, 2004). And "if deposited," they say that the sediments "can smother and bury reef benthos (Hubbard, 1986; Fabricius and Wolanski, 2000; Philipp and Fabricius, 2003)." In addition, they note that "nutrient concentrations are also often elevated inshore, which stimulates macro-algal growth (De'ath and Fabricius, 2010), increases disease prevalence (Bruno et al., 2003) and reduces coral reproduction (Koop et al., 2001)." And as a result of these several findings, they say that "these local stressors erode reef resilience, and therefore increase their vulnerability to global stressors that include ocean warming, [which is] predicted to increase the severity and intensity of coral bleaching events (Hoegh-Guldberg, 1999), ocean acidification, [which is] predicted to reduce calcification rates and reef growth (Kleypas et al., 1999), and increased storm and cyclone activity, [which is] predicted to reduce coral framework complexity and stability (Puotinen, 2004)."

What was done
In a study designed to assess the overall impact of these several reef stressors, Browne describes how "coral growth rates (linear extension, density, calcification rates) of three fast-growing corals (Acropora, Montipora, Turbinaria) were studied in situ on Middle Reef, an inshore reef located on the central Great Barrier Reef (GBR)," in order to "assess the influence of changing environmental conditions on coral condition and reef growth."

What was learned
Browne, who holds research positions in both Australia and Singapore, reports finding that "despite local anthropogenic pressures and global climate change, Middle Reef has a robust and resilient coral community," noting that "Acropora linear extension rates were comparable with rates observed at similar depths and sea surface temperatures on mid to offshore reefs on the GBR, and in the Caribbean," while additionally indicating that "Montipora and Turbinaria are abundant on inshore turbid reefs due to their adaptive capacities and are therefore an important source of carbonate for reef growth and development." In fact, Browne writes that "Montipora linear extension was greater than current estimates available, and Turbinaria, although characterized by slow linear extension, had a dense skeleton and hence may be more resilient to physical damage as ocean pH falls." And of both of them, Browne states that although they "may be more susceptible during the warmer months due to multiple stressors, they were able to rapidly recover during the cooler months."

What it means
"In summary," as Browne concludes, "corals on Middle Reef are robust and resilient to their marginal environmental conditions."

Anthony, K.R.N. and Connolly, S.R. 2004. Environmental limits to growth: physiological niche boundaries of corals along turbidity:light gradients. Oecologia 141: 373-384.

Bruno, J.F., Petes, L.E., Harvell, C.D. and Hettinger, A. 2003. Nutrient enrichment can increase the severity of coral diseases. Ecology Letters 6: 1056-1061.

De'ath, G. and Fabricius, K. 2010. Water quality as a regional driver of coral biodiversity and microalgae on the Great Barrier Reef. Ecological Applications 20: 840-850.

Fabricius, K.E. and Wolanski, E. 2000. Rapid smothering of coral reef organisms by muddy marine snow. Estuarine, Coastal and Shelf Sciences 50: 115-120.

Hoegh-Guldberg, O. 1999. Climate change, coral bleaching and the future of the world's coral reefs. Marine and Freshwater Research 50: 839-866.

Hubbard, D.K. 1986. Sedimentation as a control on reef development: St. Croix, U.S.V.I. Coral Reefs 5: 117-125.

Kleypas, J.A., Buddemeier, R.W., Archer, D., Gattuso, J.P., Langdon, C. and Opdyke, B.N. 1999. Geochemical consequences of increased atmospheric carbon dioxide on coral reefs. Science 284: 118-120.

Koop, K., Booth, D., Broadbents, A., Brodie, J., Bucher, D., Capone, D., Coll, J., Dennison, W., Erdmann, M., Harrison, P., Hoegh-Guldberg, O., Hutchings, P., Jones, G.B., Larkum, W.D., O'Neil, J., Stevens, A., Tentori, E., Ward, S., Williamson, J., and Yellowlees, D. 2001. The effects of nutrient enrichment on coral reefs. Synthesis of results and conclusions. Marine Pollution Bulletin 42: 91-120.

Lough, J.M. and Barnes, D.J. 2000. Environmental controls on growth of the massive coral Porites. Journal of Experimental Marine Biology and Ecology 245: 225-243.

Philipp, E. and Fabricius, K. 2003. Photophysiological stress in scleractinian corals in response to short-term sedimentation. Journal of Experimental Marine Biology and Ecology 287: 57-78.

Puotinen, M.L. 2004. Tropical Cyclone Impacts on Coral Reef Communities: Modeling the Disturbance Regime in the Great Barrier Reef Region, 1969-2003. Ph.D. Thesis. James Cook University, Townsville, Queensland, Australia.

Reviewed 24 October 2012