文章基本信息

标题：pH homeostasis during coral calcification in a free ocean CO2 enrichment (FOCE) experiment, Heron Island reef flat, Great Barrier Reef
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作者：Lucy Georgiou ; James Falter ; Julie Trotter 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：43
页码：13219-13224
DOI：10.1073/pnas.1505586112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceIn situ free ocean CO2 enrichment (FOCE) experiments and geochemical analyses ({delta}11B, Sr/Ca) conducted on corals (Porites cylindrica) from the highly dynamic Heron Island reef flat of the Great Barrier Reef show that this species exerts strong physiological controls on the pH of their calcifying fluid (pHcf). Over an [~]6-mo period, from mid-winter to early summer, we show that these corals maintained their pHcf at near constant elevated levels independent of the highly variable temperatures and FOCE-controlled carbonate chemistries to which they were exposed, implying they have a high degree of tolerance to ocean acidification. Geochemical analyses ({delta}11B and Sr/Ca) are reported for the coral Porites cylindrica grown within a free ocean carbon enrichment (FOCE) experiment, conducted on the Heron Island reef flat (Great Barrier Reef) for a 6-mo period from June to early December 2010. The FOCE experiment was designed to simulate the effects of CO2-driven acidification predicted to occur by the end of this century (scenario RCP4.5) while simultaneously maintaining the exposure of corals to natural variations in their environment under in situ conditions. Analyses of skeletal growth (measured from extension rates and skeletal density) showed no systematic differences between low-pH FOCE treatments ({Delta}pH = [~]-0.05 to -0.25 units below ambient) and present day controls ({Delta}pH = 0) for calcification rates or the pH of the calcifying fluid (pHcf); the latter was derived from boron isotopic compositions ({delta}11B) of the coral skeleton. Furthermore, individual nubbins exhibited near constant {delta}11B compositions along their primary apical growth axes ({+/-}0.02 pHcf units) regardless of the season or treatment. Thus, under the highly dynamic conditions of the Heron Island reef flat, P. cylindrica up-regulated the pH of its calcifying fluid (pHcf [~]8.4-8.6), with each nubbin having near-constant pHcf values independent of the large natural seasonal fluctuations of the reef flat waters (pH [~]7.7 to [~]8.3) or the superimposed FOCE treatments. This newly discovered phenomenon of pH homeostasis during calcification indicates that coral living in highly dynamic environments exert strong physiological controls on the carbonate chemistry of their calcifying fluid, implying a high degree of resilience to ocean acidification within the investigated ranges.
关键词：ocean acidification ; FOCE ; Heron Island ; coral resilience ; pH up-regulation