Nearshore Benthic-Pelagic Coupling: Coral Growth Responses to Internal Tidal Forcing on Florida Keys Coral Reefs

近岸底栖-远洋耦合：珊瑚生长对佛罗里达群岛珊瑚礁内潮汐强迫的响应

• 批准号: 9986547
• 负责人: James Leichter
• 金额: $ 34.54万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-03-15 至 2002-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9986547&HistoricalAwards=false
• 关键词: Nearshore; Benthic; Pelagic; Coupling; Coral

Internal bores generated by internal tides and breaking internal waves represent an important source of physical variability and cross-shelf transport in a range of near-shore marine environments, including the slopes of coral reefs in the Florida Keys, USA. The arrival of internal bores is marked by rapid fluctuations in near-bottom water temperature and density coupled to the onset of strong upslope flows. Cool subsurface water is forced onshore at semi-diurnal frequencies throughout the summer months, and the penetration of cool water and the high frequency physical variability associated with this pulsing mechanism decreases with distance up reef slopes. The arrival of subsurface waters on reef slopes is associated with increases in concentrations of dissolved nutrients, phytoplankton and zooplankton. Internal tidal forcing represents a suite of physical mechanisms that can potentially connect near-shore benthic communities to water and materials associated with offshore thermocline and associated subsurface chlorophyll maximum layers. The impact of internal tidal forcing is widespread throughout reefs in the Florida Keys, and new observations show that very large internal bores can be detected near the bottom at 50 m depth at least 1.5 km seaward of the Keys reef tract. The timing of these large internal bores appears to correspond to upward deviations of offshore isotherms indicative of subsurface intrusions of cool water onto the shelf seaward of the reef tract. This upwelling of isotherms may be caused by offshore meanders of the Florida Current, suggesting a direct link between regional oceanographic variability and high frequency cross-shelf transport.This project will be an investigation of the effects of internal tidal forcing on growth rates of suspension-feeding corals, as well as an examination of the roles of oceanographic variability in modulating internal tidal forcing along the Florida Keys reef tract. Two reef sites have been identified where natural topographic features produce adjacent reef slope microhabitats with equivalent depth gradients and similar overlying ambient water masses but with very different levels of exposure to internal tidal forcing. At these paired sites, manipulative coral growth rate experiments and analysis of skeletal banding patterns in native coral colonies will be combined with high frequency near-bottom physical sampling, measurement of fluxes of dissolved nutrients, and characterization of zooplankton availability. Results from experimental work will be considered within a context of broad-scale biological patterns, and regional-scale observations of high frequency oceanographic processes that can modulate internal tidal forcing. Understanding the biological and ecological importance of internal tidal forcing is limited, in part, by a lack of experimental studies and long-term, broad-scale observations. In addition to influencing thermal and nutrient dynamics, cross shelf transport associated with internal tidal bores may represent a dynamic conduit for delivery of larval invertebrates and fish to coral reefs. Such mechanisms of benthic-pelagic coupling have far-reaching potential consequences for biological processes on coral reefs and for connectivity among meta-populations distributed alongshore. Internal tidal forcing can directly influence small scale, high frequency physical variability within reefs, and may be modulated by regional scale oceanographic processes of water column stratification and alongshore currents. These forcing mechanisms, thus, may function to link small-scale, benthic biological processes to regional-scale oceanographic variability. This project should expand understanding both of coral responses to internal tidal forcing and of the importance of alongshore variability in internal tidal forcing for benthic marine communities.

内潮和破碎内波产生的内孔是一系列近岸海洋环境中物理变异和跨大陆架迁移的重要来源，包括美国佛罗里达礁群的珊瑚礁斜坡。内孔的到来是由近底层水的温度和密度的快速波动耦合到强大的上坡流的发病标志。凉爽的地下水被迫在岸上在整个夏季的半日频率，冷水的渗透和高频率的物理变化与这种脉冲机制减少与距离的珊瑚礁斜坡。次表层沃茨到达礁坡时，溶解营养盐、浮游植物和浮游动物的浓度增加。内部潮汐力是一套物理机制，可潜在地将近岸底栖生物群落与与近海温跃层和相关的次表层叶绿素最大层相关的水和物质联系起来。内部潮汐力的影响广泛存在于佛罗里达礁群的整个珊瑚礁中，新的观察结果表明，在礁群珊瑚礁区向海至少1.5公里处50 m深处的底部附近可以检测到非常大的内部钻孔。这些大的内部钻孔的时间似乎对应于离岸等温线的向上偏差，表明冷水的地下入侵到陆架向海的礁道。这种上升流的等温线可能是由近海曲流的佛罗里达电流，区域海洋学的变化和高频率的跨大陆架transportation.This项目之间的直接联系将是一个调查的影响内部潮汐强迫悬浮喂养珊瑚的生长速度，以及检查海洋学的变化在调制内部潮汐强迫沿着佛罗里达礁域的作用。两个珊瑚礁网站已被确定的自然地形特征产生相邻的礁坡微生境相同的深度梯度和类似的上覆环境水体，但有非常不同的内部潮汐力的暴露水平。在这些配对的地点，将把人工珊瑚生长率实验和对原生珊瑚群落骨骼带型的分析与高频率的近海底物理采样、溶解营养物通量测量和浮游动物可用性的表征相结合。实验工作的结果将被认为是在大规模的生物模式的背景下，高频率的海洋学过程，可以调节内部潮汐力的区域尺度观测。由于缺乏实验研究和长期、大规模的观测，对内潮强迫的生物学和生态学重要性的理解是有限的。除了影响热量和营养物动态外，与内部涌潮有关的跨大陆架迁移可能是将无脊椎动物幼虫和鱼类运送到珊瑚礁的动态管道。这种底栖-中上层耦合机制对珊瑚礁的生物过程和沿岸分布的集合种群之间的联系具有深远的潜在影响。内潮汐力可以直接影响小尺度，高频率的物理变化的珊瑚礁，并可能调制的水柱分层和沿岸流的区域尺度海洋学过程。因此，这些强迫机制可能发挥作用，将小规模的底栖生物过程与区域规模的海洋学变化联系起来。该项目应扩大了解珊瑚对内部潮汐力的反应以及内部潮汐力的沿岸变化对底栖海洋群落的重要性。