Collaborative Research: Hydrodynamic Forcing of Metabolism of Coral Reef Algal Communities (RUI)

木匠9314470解释珊瑚礁如何维持高生物量和极高的总初级生产力的当前范例是，珊瑚礁内发生了营养物质和有机物的紧密循环，导致净自养区域和净异养区域交替出现。自养上游群落被认为支持下游异养群落，总体平衡，导致生态系统P/R比接近于1。根据这一范例，珊瑚礁与周围的营养稀少的海洋没有明显的耦合。最近的研究表明，珊瑚礁可能比目前认为的更依赖水动力过程。尽管热带水域的营养物质浓度很低，但大量的水平流穿过珊瑚礁，可能导致大量营养物质流向海底初级生产者。主要的上游自养带是礁滩，那里的藻类草皮组合负责大部分初级生产力。前人的工作表明，水流速度对藻类草坪的初级生产力和固氮率有显著影响。此外，在一个礁石上的水流测量表明，藻类树冠高度显著改变了当地的水动力状况，因此，藻类草坪的代谢过程在很大程度上可能是扩散受限的。该项目将检验珊瑚礁藻类草坪的初级生产力和固氮率受扩散限制的假设。将对礁滩上的流动环境进行测量，并用来估计在树冠高度上变化的藻类草皮受到扩散限制的程度。然后，该项目将继续测试有关导致扩散限制的特定因素的假设。这个项目的结果应该会填补珊瑚礁环境中水流的经验测量以及水流如何影响藻类新陈代谢的空白。这项研究的结果可能会导致对珊瑚礁功能的理解发生重大的范式转变。表明珊瑚礁是与周围海洋环境紧密耦合的开放生态系统，将对预测全球气候变化对这些独特生态系统的影响产生重要影响。***

Carpenter 9314470 The current paradigm explaining how coral reefs maintain high biomass of organisms and extremely high rates of gross primary productivity is that tight recycling of nutrients and organic matter occurs within the reef resulting in zones of net autotrophy alternating with zones of net heterotrophy. Autotrophic upstream communities are thought to support downstream heterotrophic assemblages with the overall balance resulting in ecosystem P/R ratios near unity. According to this paradigm, coral reefs are not coupled significantly to the surrounding oligotrophic ocean. Recent studies suggest that coral reefs may be much more dependent on hydrodynamic processes than currently believed. Although nutrient concentrations of tropical waters are very low, an enormous volume of water is advected across the reef and could result in a large flux of nutrients to benthic primary producers. The major upstream autotrophic zone is the reef flat where algal turf assemblages are responsible for the majority of primary productivity. Previous work has demonstrated that rates of primary productivity and nitrogen fixation of algal turf are affected significantly by water flow speed. Furthermore, flow measurements on one reef suggest that algal canopy height significantly alters the local hydrodynamic regime and as a result, metabolic processes of algal turfs may be diffusion-limited for a significant proportion of time. This project will test the hypothesis that rates of primary productivity and nitrogen fixation of coral reef algal turfs are diffusion-limited. Measurements of the flow environment on a reef flat will be made and used to estimate the degree to which algal turfs varying in canopy height are diffusion-limited. The project will then move on to test hypotheses about the specific factors that result in diffusion-limitation. The results of this project should fill a gap on empirical measurements of water flow in coral reef environments and how wate r flow affects algal metabolism. The results of this research may lead to a significant paradigm shift in understanding how coral reefs function. Demonstration that reefs are open ecosystems that are strongly coupled to the surrounding ocean environment would have important implications for predictions of the effects of global climate change on these unique ecosystems. ***