Corals may be better able to cope with ocean acidification than previously believed, according to new research published in Nature Climate Change, providing a glimmer of hope for the future of coral reefs.
As more carbon dioxide enters the atmosphere from the burning of fossil fuels, more carbon dioxide is dissolved in the ocean, lowering the pH of the water. This process, known as ocean acidification, is occurring at an unprecedented rate. This is causing problems for shell-building organisms, and it raises concerns for corals. Can corals and their symbiotic algae have the ability to adapt or acclimate to such rapid changes in ocean chemistry?
An international scientific team has identified a built-in mechanism that could equip some species of coral and their symbiotic algae to reduce the negative impacts of ocean acidification. They found that stony corals, such as Porites and Acropora, have molecular ‘pumps’ at their site of calcification, allowing them to regulate their internal pH balance. The internal pH changes are approximately one-half of those in the surrounding seawater.
The other good news is that there doesn't seem to be much of a fitness cost—the stony corals’ pH-buffering capacity enables them to increase their rate of calcification at little additional energy cost. For example, corals with symbiotic algae use less than one percent of the energy generated by photosynthesis in order to buffer pH.
The ability to regulate pH differs among species and is completely absent in some marine calcifying organisms. Those organisms with minimal or no ability to regulate their pH will suffer substantial decreases in skeletal growth rates as oceans become more acidic. Still, this is a positive indication that at least some coral species don't fall in this latter group.
Although the researchers conclude that pH regulation at the site of calcification provides corals with enhanced resilience to the effects of ocean acidification, they note that the overall health of coral reef ecosystems is dependent upon multiple factors. The combined effects of increased thermal stress from global warming and local environmental impacts such as terrestrial runoff, pollution, and overfishing could still cause problems for these corals even if acidification doesn't.