Posted on | September 2, 2011 | Comments Off
Paul Jokiel, a researcher at the Hawaiʻi Institute of Marine Biology, has come up with a new explanation for the effects of ocean acidification on coral reefs.
Since the beginning of the Industrial Revolution, the concentration of carbon dioxide in the atmosphere has been rising due to the burning of fossil fuels. Increased absorption of this carbon by the ocean is lowering the seawater pH and aragonite saturation state in a process known as ocean acidification. Aragonite is the mineral form of calcium carbonate that is laid down by corals to build their hard skeleton.
Numerous studies have shown a direct correlation between increased acidification, aragonite saturation and declining coral growth, but the process is not well understood and various experiments have led to opposing conclusions. A recent reanalysis by Jokiel suggests that the primary effect of ocean acidification on coral growth is to interfere with the transfer of hydrogen ions between the water column and the coral tissue. His proton flux hypothesis offers an explanation for the reduction in calcification of corals caused by ocean acidification.
In the past, scientists have focused on processes at the coral tissues. The alternative provided by Jokiel’s proton flux hypothesis is that calcification of coral skeletons are dependent on the passage of hydrogen ions between the water column and the coral tissue. This process ultimately disrupts corals’ ability to create an aragonite skeleton. Lowered calcification rates are problematic for coral reefs because it creates weakened coral skeletons leaving them susceptible to breakage, and decreasing protection.
This hypothesis does not change the general conclusions that increased ocean acidification is lowering coral growth throughout the world, but provides new insights into the importance of ocean acidification and temperature on coral reefs. “The model is a radical departure from previous thought, but is consistent with existing observations and warrants testing in future studies,” says Jokiel.