Corals In Acid


As atmospheric CO2 increases, the ocean will become more acidic. The oceans are known to absorb about 1/3 of the CO2 we put into the air. Current projections indicate the pH of the ocean will drop by 1.4 over the next 300 years. Now keep in mind this is on a log-scale so the current ph of the ocean is between 8-8.3, which corresponds to 1/10 concentration of hydrogen ions. A drop of 1.4 puts the pH at 6.6-6.9 closer to hydrogen ion concentration of 10. This is between a 10x-100x increase in acidity.

When CO2 dissolves and reacts with water it can from three chemical species: 1) dissolved carbon dioxide, carbonic acid (H2CO3), bicarbonate (HCO3-), and carbonate (CO32-). The ratio depends on temperature and alkalinity. The short is that increasing CO2 results in increased carbonic acid causing a reduction of carbonate ions necessary for corals and snails, among other invertebrates.

A recent Brevia in Science indicates that skeleton-producing corals can actually survive these acidic conditions maintaining basic life functions including reproduction. In the experiments after one month total skeleton dissolution occurred. The polyps themselves however elongated, dissociated from the colony, and affixed to hard substrate. Indeed, polyp biomass increased 3x that of polyps associated with calcified colonies. After 1 year, the solitary polyps were transferred back to normal conditions where the calcified and reformed colonies. Compared to organisms that survived mass extinction events by seeking geographic localities with favorable conditions, geographical refugia, the authors suggest that corals may use physiological refugia, switching between hard and soft forms, to survive stressful conditions.

Dr. M (1801 Posts)

Craig McClain is the Executive Director of the Lousiana University Marine Consortium. He has conducted deep-sea research for 20 years and published over 50 papers in the area. He has participated in and led dozens of oceanographic expeditions taken him to the Antarctic and the most remote regions of the Pacific and Atlantic. Craig’s research focuses on how energy drives the biology of marine invertebrates from individuals to ecosystems, specifically, seeking to uncover how organisms are adapted to different levels of carbon availability, i.e. food, and how this determines the kinds and number of species in different parts of the oceans. Additionally, Craig is obsessed with the size of things. Sometimes this translated into actually scientific research. Craig’s research has been featured on National Public Radio, Discovery Channel, Fox News, National Geographic and ABC News. In addition to his scientific research, Craig also advocates the need for scientists to connect with the public and is the founder and chief editor of the acclaimed Deep-Sea News (, a popular ocean-themed blog that has won numerous awards. His writing has been featured in Cosmos, Science Illustrated, American Scientist, Wired, Mental Floss, and the Open Lab: The Best Science Writing on the Web.