Seawater carbonate chemistry and calcification rate during mesocosm experiments with coral Montipora capitata, 2008@en

A long-term (10 months) controlled experiment was conducted to test the impact of increased partial pressure of carbon dioxide (pCO2) on common calcifying coral reef organisms. The experiment was conducted in replicate continuous flow coral reef mesocosms flushed with unfiltered 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 µatm (mean ± sd)]. Acidification had a profound 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 as rhodoliths living in the control mesocosms grew at a rate of 0.6 g buoyant weight per year while those in the acidified experimental treatment decreased in weight at a rate of 0.9 g buoyant weight per year, representing a 250% difference. 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.本研究开展了一项为期10个月的受控实验，以探究二氧化碳分压（partial pressure of carbon dioxide, pCO2）升高对常见钙化珊瑚礁生物的影响。本实验于夏威夷瓦胡岛卡内奥赫湾（Kaneohe Bay）的未过滤海水补给的重复连续流珊瑚礁中宇宙系统（mesocosms）中开展，所有中宇宙系统均置于全日照环境下，可模拟邻近礁坪的温度与海水化学特征的昼夜及季节波动。处理组中宇宙系统通过调控将pCO2提升至本世纪预期水平，其中正午时分pCO2较对照组高出365±130微标准大气压（µatm，均值±标准差（standard deviation, sd））。海水酸化对壳状珊瑚藻（crustose coralline algae, CCA）种群的发育与生长产生了深远影响，实验期间对照组中宇宙系统内的CCA盖度可达25%，而酸化组仅为4%，相对覆盖率降低86%；自由生活的CCA类群即珊瑚藻结球（rhodoliths），对照组中的结球年漂浮重量增长0.6克，而酸化处理组中的结球年漂浮重量下降0.9克，两者差异达250%。壳状珊瑚藻在碳酸盐礁体的形成与稳定中发挥关键作用，因此此类程度的未来环境变化可能对全球珊瑚礁造成严重影响，酸化条件下珊瑚的钙化作用下降15%~20%，在一项实验中酸化条件下珊瑚的线性生长速率下降14%，指状鹿角珊瑚（Pocillopora damicornis）的幼虫可在酸化条件下成功附着定居，此外经6个月的处理暴露后，团块微孔珊瑚（Montipora capitata）的配子生成量无显著差异。