CO2 in oceans no threat to corals

Many marine organisms need CO2 to make their coral skeletons, carbonate shells and so on. Corals also have symbiotic plants within their flesh that use CO2 in photosynthesis.

Marine life flourishes where CO2 is abundant. Professor Walter Stark wrote about a favourite place for scuba divers, the ‘Bubble Bath’ near Dobu Island, Papua New Guinea. Here CO2 of volcanic origin is bubbling visibly through the water so that the water is saturated with CO2. Abundant life flourishes to make the spot a spectacular diver’s delight. He reported many accurate measurements of pH in the area and concluded “It seems that coral reefs are thriving at pH levels well below the most alarming projections for 2100.”

One of the factors affecting ocean pH is photosynthesis by plants. Experimental results show that plants grow better if CO2 is increased, and greenhouse managers commonly increase the CO2 artificially to increase crops, often by 30% or more. There is every reason to suppose that marine plants also thrive if CO2 is increased. There is also experimental evidence that carbonate secreting animals thrive in higher CO2. Herfort and colleagues concluded that the likely result of human emissions of CO2 would be an increase in oceanic CO2 that could stimulate photosynthesis and calcification in a wide variety of corals.

Marine life, including that part that fixes CO2 as the carbonate in limestones such as coral reefs, evolved on an Earth with CO2 levels many times higher than those of today, as reported by Berner and Kothaval. It may be true to say that today’s marine life is getting by in a CO2-deprived environment.

Tuvalu has long been ‘hot news’ as the favourite island to be doomed by sea level rise driven by global warming, allegedly caused in turn by anthropogenic carbon dioxide. But if a coral island is sinking slowly (or relative sea level rising slowly) the growth of coral can keep up with it. In the right circumstances some corals can grow over 2 cm in a year, but growth rate depends on many factors. Coral islands, made of living things, are not static dip-sticks against which sea level can be measured. We have to consider coral growth, erosion, transport and deposition of sediment and many other aspects of coral island evolution – not just the pH of seawater.

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