Hawaii Institute of Marine Biology, University of Hawaii , Kaneohe, HI , United States.
PeerJ. 2014 May 22;2:e378. doi: 10.7717/peerj.378. eCollection 2014.
Precise measurements were conducted in continuous flow seawater mesocosms located in full sunlight that compared metabolic response of coral, coral-macroalgae and macroalgae systems over a diurnal cycle. Irradiance controlled net photosynthesis (P net), which in turn drove net calcification (G net), and altered pH. P net exerted the dominant control on [CO3 (2-)] and aragonite saturation state (Ωarag) over the diel cycle. Dark calcification rate decreased after sunset, reaching zero near midnight followed by an increasing rate that peaked at 03:00 h. Changes in Ωarag and pH lagged behind G net throughout the daily cycle by two or more hours. The flux rate P net was the primary driver of calcification. Daytime coral metabolism rapidly removes dissolved inorganic carbon (DIC) from the bulk seawater and photosynthesis provides the energy that drives G net while increasing the bulk water pH. These relationships result in a correlation between G net and Ωarag, with Ωarag as the dependent variable. High rates of H(+) efflux continued for several hours following mid-day peak G net suggesting that corals have difficulty in shedding waste protons as described by the Proton Flux Hypothesis. DIC flux (uptake) followed P net and G net and dropped off rapidly following peak P net and peak G net indicating that corals can cope more effectively with the problem of limited DIC supply compared to the problem of eliminating H(+). Over a 24 h period the plot of total alkalinity (AT ) versus DIC as well as the plot of G net versus Ωarag revealed a circular hysteresis pattern over the diel cycle in the coral and coral-algae mesocosms, but not the macroalgae mesocosm. Presence of macroalgae did not change G net of the corals, but altered the relationship between Ωarag and G net. Predictive models of how future global changes will effect coral growth that are based on oceanic Ωarag must include the influence of future localized P net on G net and changes in rate of reef carbonate dissolution. The correlation between Ωarag and G net over the diel cycle is simply the response of the CO2-carbonate system to increased pH as photosynthesis shifts the equilibria and increases the [CO3 (2-)] relative to the other DIC components of [HCO3 (-)] and [CO2]. Therefore Ωarag closely tracked pH as an effect of changes in P net, which also drove changes in G net. Measurements of DIC flux and H(+) flux are far more useful than concentrations in describing coral metabolism dynamics. Coral reefs are systems that exist in constant disequilibrium with the water column.
在全日照的连续流动海水中中进行了精确测量，这些中进行了精确测量位于全日照的连续流动海水中中进行了精确测量，比较了珊瑚、珊瑚-海藻和海藻系统在昼夜周期内的代谢反应。光照控制净光合作用 (Pnet)，进而驱动净钙化 (Gnet)，并改变 pH 值。Pnet 在昼夜周期内对[CO3(2-)]和方解石饱和度 (Ωarag) 起主导控制作用。日落后暗钙化速率下降，午夜附近接近零，然后以 03:00 h 达到峰值的速率增加。在整个日周期中，Ωarag 和 pH 值滞后于 Gnet 两个多小时。净光合作用率 Pnet 是钙化的主要驱动因素。白天，珊瑚会从海水中快速去除溶解无机碳 (DIC)，光合作用提供能量，驱动 Gnet，同时增加水体 pH 值。这些关系导致 Gnet 和 Ωarag 之间存在相关性，其中 Ωarag 是因变量。在中值之后，Gnet 达到峰值，高 H(+) 通量继续持续数小时+）净光合作用率 suggesting 珊瑚很难像质子通量假说所描述的那样排出代谢废物质子。DIC 通量 (吸收) 紧随 Pnet 和 Gnet 之后，在 Pnet 和 Gnet 达到峰值后迅速下降，表明与消除 H(+) 相比，珊瑚可以更有效地应对有限 DIC 供应的问题。在 24 小时的时间里，总碱度 (AT) 与 DIC 的关系图以及 Gnet 与 Ωarag 的关系图显示，在珊瑚和珊瑚-海藻中，昼夜周期内出现了圆形滞后模式，但在海藻中则没有。海藻的存在并没有改变珊瑚的 Gnet，但改变了 Ωarag 和 Gnet 之间的关系。基于海洋 Ωarag 预测未来全球变化如何影响珊瑚生长的模型必须包括未来局部 Pnet 对 Gnet 的影响以及珊瑚礁碳酸盐溶解速率的变化。昼夜周期内 Ωarag 和 Gnet 之间的相关性仅仅是光合作用使平衡向增加 [CO3(2-)] 方向移动，增加相对于 [HCO3(-)] 和 [CO2] 的其他 DIC 成分的 [CO3(2-)] 时，二氧化碳-碳酸盐系统对 pH 值升高的响应。因此，Ωarag 作为 Pnet 变化的影响，与 pH 值密切相关，这也导致了 Gnet 的变化。与浓度相比，DIC 通量和 H(+) 通量的测量在描述珊瑚代谢动力学方面更有用。珊瑚礁是与水柱处于不平衡状态的系统。
