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Mass transfer limitation of photosynthesis of coral reef algal turfs

机译：珊瑚礁藻类光合作用的传质限制

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Algal turfs are the major primary produclng component on many coral reefs and this production supports higher levels in the complex reef trophic web. Rates of metabolism of algal turfs are related positively to water motion, consistent with limitation by the diffusion of a substance through a boundary layer. Based on engineering mass transfer theory, we hypothesized that photosynthesis of algal turfs is controlled by rates of mass transfer and responses of photosynthesis to increasing flow speed should be predicted by engineering correlations. This hypothesis was tested in ten experiments where photosynthesis was estimated in a flume/respirometer from changes in dissolved oxygen at eight flow speeds between 0.08 and 0.52 m/s. Flow in the flume and over the reef at Kaneohe Bay, Oahu, Hawaii was estimated using hot-film thermistor and electromagnetic current meters. Rates of photosynthesis were related positively to flow in all experiments and plots of the log of the average Sherwood number (Sh_(meas)) versus log Reynolds number (Re_D) for each experiment are lower than predicted for mass transfer through a turbulent boundary layer. Algal turf-covered plates are characterized as hydrodynamically transitional to fully rough surfaces and the lower than predicted slopes suggest that roughness reduces rates of mass transfer. A negative correlation between algal turf biomass and slopes of the log Sh_(meas)-log Re_D plots suggests that mass transfer to algal turfs is affected significantly by the physical structure of the algal community. Patterns of photosynthesis based on changes in dissolved oxygen and dissolved inorganic carbon concentrations (DIC) indicate that the flow speed effect is not the result of increased flux of oxygen from the algal turfs, and combined with the short response time to flow speed, suggest that DIC may limit rates of photosynthesis. Although there are differences between flow in the flume and flow over algal turfs on the reef, these results suggest that photosynthesis is controlled, at least in part, by mass transfer. The chemical engineering approach provides a framework to pose further testable hypotheses about how algal canopy height, flow osclllation, turbulence, and substratum roughness may modulate rates of metabolism of coral reef algal turfs.
机译：藻类草皮是许多珊瑚礁中的主要主要生产成分，这种生产支持复杂珊瑚礁营养网中较高的含量。藻类草皮的新陈代谢速率与水运动呈正相关，这与物质通过边界层扩散的限制相一致。基于工程传质理论，我们假设藻类草皮的光合作用受传质速率控制，并且光合对增加流速的响应应通过工程相关性进行预测。在10个实验中测试了该假设，其中在水槽/呼吸计中根据0.08至0.52 m / s的八种流速下溶解氧的变化估算了光合作用。使用热膜热敏电阻和电磁电流表估算了夏威夷瓦胡岛卡尼奥赫湾水槽和礁石上的流量。在所有实验中，光合作用的速率与流量呈正相关，并且每个实验的平均舍伍德数（Sh_（meas））对数雷诺数（Re_D）的对数图低于通过湍流边界层传质的预测值。藻类覆盖的板块的特征是流体动力学过渡到完全粗糙的表面，低于预期的斜率表明粗糙度降低了传质速率。藻类草坪生物量与log Sh_（meas）-log Re_D图的斜率之间存在负相关关系，这表明藻类群落的物理结构显着影响了向藻类草坪的传质。基于溶解氧和溶解无机碳浓度（DIC）变化的光合作用模式表明，流速效应不是藻类草皮中氧气通量增加的结果，并且结合了对流速的短响应时间，表明DIC可能会限制光合作用的速率。尽管水槽中的水流与礁石上的藻类水流之间存在差异，但这些结果表明，光合作用至少部分受传质控制。化学工程方法提供了一个框架，可以提出关于海藻冠层高度，水流振荡，湍流和基质粗糙度如何调节珊瑚礁海藻草皮新陈代谢速率的进一步可检验的假设。

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