A long-term (10 months) controlled experiment was conducted to test the impact of increased partial pres- sure of carbon dioxide (pCO2) on common calcifying coral reef organisms. The experiment was conducted in replicate continuous flow coral reef mesocosms flushed with unfil- tered sea water from Kaneohe Bay, Oahu, Hawaii. Mesocosms were located in full sunlight and experienced diurnal and seasonal fluctuations in temperature and sea water chemistry characteristic of the adjacent reef flat. Treatment mesocosms were manipulated to simulate an increase in pCO2 to levels expected in this century [midday pCO2 levels exceeding control mesocosms by 365 ± 130 latm (mean ± sd)]. Acidification had a pro- found impact on the development and growth of crustose coralline algae (CCA) populations. During the experiment, CCA developed 25% cover in the control mesocosms and only 4% in the acidified mesocosms, representing an 86% relative reduction. Free-living associations of CCA known Communicated by Guest Editor Dr. Katharina Fabricius. P. L. Jokiel (&) ? K. S. Rodgers ? E. F. Cox Hawai‘i Coral Reef Assessment and Monitoring Program, Hawai‘i Institute of Marine Biology, P.O. Box 1346, Kaneohe, HI 96744, USA e-mail: email@example.com I. B. Kuffner U.S. Geological Survey, Florida Integrated Science Center, St. Petersburg, FL 33701, USA A. J. Andersson Bermuda Institute of Ocean Sciences, 17 Biological Lane, St. George’s GE01, Bermuda F. T. Mackenzie Department of Oceanography, University of Hawai‘i, 1000 Pope Road, Honolulu, HI 96822, USA as rhodoliths living in the control mesocosms grew at a rate of 0.6 g buoyant weight year-1 while those in the acidified experimental treatment decreased in weight at a rate of 0.9 g buoyant weight year-1, representing a 250% differ- ence. CCA play an important role in the growth and stabilization of carbonate reefs, so future changes of this magnitude could greatly impact coral reefs throughout the world. Coral calcification decreased between 15% and 20% under acidified conditions. Linear extension decreased by 14% under acidified conditions in one experiment. Larvae of the coral Pocillopora damicornis were able to recruit under the acidified conditions. In addition, there was no significant difference in production of gametes by the coral Montipora capitata after 6 months of exposure to the treatments.
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