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

目前解释珊瑚礁如何保持生物的高生物量和极高的总初级生产力的范式是，在珊瑚礁内发生的营养物质和有机物的紧密循环导致净自养区与净异养区交替。自养上游群落被认为支持下游异养组合，总体平衡导致生态系统P/R比接近统一。根据这种模式，珊瑚礁与周围的贫营养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于水动力过程。虽然热带水域的营养物质浓度很低，但大量的水通过珊瑚礁平流，可能导致大量营养物质流向底栖生物初级生产者。主要的上游自养带是礁滩，其中藻草组合负责大部分初级生产力。以往的研究表明，藻草皮的初级生产力和固氮速率受水流速度的显著影响。此外，在一个珊瑚礁上的流量测量表明，藻冠高度显著改变了当地的水动力状态，因此，藻草坪的代谢过程可能在相当比例的时间内受到扩散限制。本项目将检验珊瑚礁藻皮初级生产力和固氮速率受扩散限制的假设。对礁滩上的水流环境进行测量，并用于估计不同冠层高度的藻皮对扩散的限制程度。然后，该项目将继续测试导致扩散限制的具体因素的假设。该项目的研究结果将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代谢的空白。这项研究的结果可能会导致理解珊瑚礁如何运作的重大范式转变。证明珊瑚礁是开放的生态系统，与周围的海洋环境密切相关，将对预测全球气候变化对这些独特生态系统的影响具有重要意义。* * *

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. ***