School of Environmental Systems Engineering and The Oceans Institute M470, University of Western Australia, Perth,Western Australia, Australia.
PLoS One. 2013 Apr 23;8(4):e60830. doi: 10.1371/journal.pone.0060830. Print 2013.
The impact of physico-chemical factors on percent coral cover and coral health was examined on a spatial basis for two dominant Acropora species, A. digitifera and A. spicifera, at Ningaloo Reef (north-western Australia) in the southeast Indian Ocean. Coral health was investigated by measuring metabolic indices (RNA/DNA ratio and protein concentration), energy levels (lipid ratio) and autotrophic indices (chlorophyll a (chl a) and zooxanthellae density) at six stations during typical seasons (austral autumn 2010 (March and April), austral winter 2010 (August)) and during an extreme La Niña event in summer 2011 (February). These indices were correlated with 15 physico-chemical factors (measured immediately following coral sampling) to identify predictors for health indices. Variations in metabolic indices (protein concentration and RNA/DNA ratio) for A. spicifera were mainly explained by nitrogen, temperature and zooplankton concentrations under typical conditions, while for A. digitifera, light as well as phytoplankton, in particular picoeukaryotes, were important, possibly due to higher energy requirement for lipid synthesis and storage in A. digitifera. Optimum metabolic values occurred for both Acropora species at 26-28°C when autotrophic indices (chl a and zooxanthellae density) were lowest. The extreme temperature during the La Niña event resulted in a shift of feeding modes, with an increased importance of water column plankton concentrations for metabolic rates of A. digitifera and light and plankton for A. spicifera. Our results suggest that impacts of high sea surface temperatures during extreme events such as La Niña may be mitigated via reduction on metabolic rates in coral host. The high water column plankton concentrations and associated low light levels resulted in a shift towards high symbiont densities, with lower metabolic rates and energy levels than the seasonal norm for the coral host.
物理化学因素对两种优势鹿角珊瑚（A. digitifera 和 A. spicifera）的珊瑚盖度和珊瑚健康的影响，在印度洋东南部的宁格鲁珊瑚礁（澳大利亚西北部）进行了空间研究。在典型季节（2010 年秋，3 月和 4 月；2010 年冬，8 月）和 2011 年夏极端拉尼娜事件期间，在六个站点测量代谢指数（RNA/DNA 比和蛋白质浓度）、能量水平（脂质比）和自养指数（叶绿素 a (chl a) 和共生藻密度），以研究珊瑚健康。这些指数与 15 个物理化学因素（在珊瑚采样后立即测量）相关联，以确定健康指数的预测因子。在典型条件下，A. spicifera 的代谢指数（蛋白质浓度和 RNA/DNA 比）的变化主要由氮、温度和浮游动物浓度解释，而对于 A. digitifera，光以及浮游植物，特别是微微型真核生物，很重要，可能是因为 A. digitifera 合成和储存脂质需要更高的能量。当自养指数（chl a 和共生藻密度）最低时，两种鹿角珊瑚的最佳代谢值都发生在 26-28°C。拉尼娜事件期间的极端温度导致摄食模式发生变化，水柱浮游生物浓度对 A. digitifera 代谢率以及对 A. spicifera 的光和浮游生物的重要性增加。我们的研究结果表明，拉尼娜等极端事件中高海面温度的影响可能通过降低珊瑚宿主的代谢率来缓解。高水柱浮游生物浓度和相关的低光照水平导致共生藻密度增加，珊瑚宿主的代谢率和能量水平低于季节性平均值。
