Review: Fine M & Tchernov D (2007). Scleractinian coral species survive and recover from decalcification. Science, 315:1811.

Feature Paper: Fine M & Tchernov D (2007). Scleractinian coral species survive and recover from decalcification. Science, 315:1811.

Author Abstract: Anthropogenic-driven accumulation of carbon dioxide in the atmosphere and projected ocean acidification have raised concerns regarding the eventual impact on coral reefs. This study demonstrates that skeleton-producing corals grown in acidified experimental conditions are able to sustain basic life functions, including reproductive ability, in a sea anemone-like form and will resume skeleton building when reintroduced to normal modern marine conditions. These results support the existence of physiological refugia, allowing corals to alternate between nonfossilizing soft-body ecophenotypes and fossilizing skeletal forms in response to changes in ocean chemistry. This refugia, however, does not undermine the threats to reef ecosystems in a high carbon dioxide world.


Note to Readers: Follow links above for author email, full article text, or the publishing scientific journal. Author notes in my review are in quotes.


Review: This paper is one of the Science journal's "Brevia" reports. Generally, these reports are 1 page in length and provide a timely and non-jargon-filled scientific breakthroughs or accounts of wide value. Basically, they are short, important papers, often with brief and well thought out figures / images. They are very difficult to write because, as Mark Twain once said, "I'm sorry I wrote you a long letter. I didn't have the time to write a short one." Editing is the hardest job with any writing and when you must condense sometimes years of complex research into a 1-page summary, you'd be surprised how hard it can be.

This paper is important because it deals with the topic of increased ocean acidification, which is predicted over the current century as atmospheric carbon dioxide (and other greenhouse gases) increase. As a quick note though for naysayers: humans have already affected sea surface pH since the 1700s, from which we have global measurements.

[Figure showing "change in sea surface pH caused by anthropogenic carbon dioxide between the 1700s and the 1990s." Lower numbers are more acidic pH conditions from base measurements in 1700.]

Most people know that trees absorb carbon dioxide, but the oceans absorb just as much (or more) than all the trees in the world. Some of the carbon dioxide absorbed is used by phytoplankton -- microscopic plants that form the base of the food chain in the open ocean. But with excess carbon dioxide, the ocean acts as a big chemical sponge and responds to the increasing carbon dioxide by changing its pH balance. When the pH of seawater is too acidic, calcium gets dissolved. Calcium is found in a lot of living things in the ocean (basically everything with a shell or a skeleton) and if more calcium gets dissolved every day than can be accreted by the host body, then the potential for the organism to die is great (and certainly, growth is impeded or stopped).

The authors took the hypothetical situation of a high-greenhouse gas world and replicated it in the laboratory. Basically, they pumped carbon dioxide into flow-through seawater systems under otherwise natural Mediterranean Sea environmental conditions (temperature, salinity, photoperiod) and recorded changes in coral physiology in 2 species of Mediterranean corals (Oculina patagonica and Madracis pharencis) over 12 months in pH ranging from 7.3 - 7.6 (normal Mediterranean Sea water is pH 8.0 - 8.3). 

What is very surprising about the results of their study is that their corals survived but their skeletons completely dissolved. The corals went from being colonial organisms to individual polyps that looked functionally similar to sea anemones. Bleaching (or loss of symbiotic algae) occured in 20% of corals in the study but they recovered.

The take-home message is that "this has far-reaching impolications for better understanding the natural history of corals but mainly implies that corals might survive large-scale environmental change, such as that expected for the following century." 

I want to note however that just because 2 coral species (out of more than 800 total species) survived the experiment, they were functionally very different. No calcium or calcification means no reef formation. No reef formation means no ability to "grow up" towards the light as islands subside (sink) naturally or as sea levels rise (which will increase with increasing atmospheric carbon dioxide). I should also note that coral "reefs" are geologically recent even though coral "non-reefal communities" have been around since the dinosaurs. 

So yes, at least some corals will survive even under major environmental changes but in no way should people assume that the diverse coral reefs we can dive or snorkel on today will necessarily be there. 

Life goes on and nature adapts, but wouldn't it be a shame if something so beautiful were gone?

[Photo by Dave Burdick of Guam Reef Life: Gun Beach, Tumon, Guam low tide, exposed Acropora spp. corals]