Review: Kuffner IB, Andersson AJ, Jokiel PL, Rodgers KS, Mackenzie FT (2008). Decreased abundance of crustose coralline algae due to ocean acidification. Nature Geoscience, 1(2):114-117.

Feature Paper: Kuffner IB, Andersson AJ, Jokiel PL, Rodgers KS, Mackenzie FT (2008). Decreased abundance of crustose coralline algae due to ocean acidification. Nature Geoscience, 1(2):114-117.

Author Abstract: Owing to anthropogenic emissions, atmospheric concentrations of carbon dioxide could almost double between 2006 and 2100 according to business-as-usual carbon dioxide emission scenarios. Because the ocean absorbs carbon dioxide from the atmosphere, increasing atmospheric carbon dioxide concentrations will lead to increasing dissolved inorganic carbon and carbon dioxide in surface ocean waters, and hence acidification and lower carbonate saturation states. As a consequence, it has been suggested that marine calcifying organisms, for example corals, coralline algae, molluscs and foraminifera, will have difficulties producing their skeletons and shells at current rates, with potentially severe implications for marine ecosystems, including coral reefs. Here we report a seven-week experiment exploring the effects of ocean acidification on crustose coralline algae, a cosmopolitan group of calcifying algae that is ecologically important in most shallow-water habitats. Six outdoor mesocosms were continuously supplied with sea water from the adjacent reef and manipulated to simulate conditions of either ambient or elevated seawater carbon dioxide concentrations. The recruitment rate and growth of crustose coralline algae were severely inhibited in the elevated carbon dioxide mesocosms. Our findings suggest that ocean acidification due to human activities could cause significant change to benthic community structure in shallow-warm-water carbonate ecosystems.


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 important because it deals with the topic of what will happen to coral reefs as carbon dioxide increases from human greenhouse gas emissions. Unlike the previous science corner dealing directly with corals, this paper looks at calcarious crustose coralline algae (CCA). CCA are important on reefs because they:
1) Bind perhaps as much atmospheric carbon dioxide as corals do on reefs;
2) They cement reefs together by growing over adjacent rocks;
3) Coral larvae use CCA as settlement cues and when CCA aren't present, settlement can be negatively affected (as discussed in last week's other Kuffner paper).


As mentioned in last week's Science Corner, Ilsa Kuffner's lab produces high-quality marine ecology experiments based on laboratory manipulations of environmental conditions. In this experiment, they had open-system cylindrical aquaria with established populations of CCA that they exposed to elevated carbon dioxide concentrations. Following the experimental manipulation, they monitored recruitment rates, growth, and eventual decalcification of CCA populations in the flow-through systems.


Like the group studying Mediterranean hard corals (in week 7's Science Corner), Kuffner et al. found that increased carbon dioxide does decalcify their experimental organism.


This paper is important because it shows another group that will be affected as greenhouse gas concentrations continue to increase over the current century. And while the general public might not know CCA as well as corals, it is also important to note that since coral larvae use CCA as settlement cues (meaning the larvae chemically sense the CCA and preferentially choose to settle on areas of the reef with dominant CCA growth, among other ideal conditions), the lower the CCA presence (which will happen with increasing greenhouse gases, as this paper shows), the more area is left for other algae and marine organisms, which will all combine to lessen coral recruitment.


The take-home message is that coral can be affected by more than just direct impediments to their survival; they can be affected by changes in their immediate environment. The purpose of ecological studies is to show that organisms are often interdependent upon each other and certain environmental conditions in order to properly thrive. Once one "leg" is affected, the whole house of cards can fall down so to speak.


Now that we've discussed several aspects of coral reef decline, next we'll examine the case of what happens after a coral reef is already degraded. How can managers help recover damaged coral reefs to their once-former glory?