An accurate representation of physical and biological processes is crucial to resolve larval dispersal pathways and characterize connectivity of coral reef ecosystems. We investigate how hydrodynamic forcings drive larval retention rates during the bi-annual mass coral spawning of the coral genus Acropora within a coral reef atoll (Mermaid Reef), located off northwestern Australia. By analyzing hydrodynamic conditions during 41 yr of historical spring and autumn coral spawning events, we identify typical and extreme hydrodynamic forcing conditions. Particle tracking using the output from a fine-scale coupled wave-flow hydrodynamic model forced with typical hydrodynamic conditions during coral spawning, revealed a mean transport of larvae eastward across the atoll. Transport was mainly driven by a combination of wave and tidal currents, where the residual tidal flow and unidirectional wave flow increased the net export of particles, and the oscillatory tidal (non-residual) flow reduced the net export of particles from the reef. Importantly, however, numerical simulations forced with extreme hydrodynamic conditions generated by episodic tropical cyclones (11 out of 41 yr) showed large deviations from the typical eastward flow during autumn spawning, generating different connectivity pathways within the reef. Considering the substantial time larvae can be retained within reef systems, overlooking fine-scale hydrodynamic processes may greatly overestimate larval transport distances between adjacent coral reef atolls. As a result, we emphasize the need to consider fine-scale hydrodynamic processes within regional connectivity predictions, which is generally not considered yet critical to understand the capacity of reefs to recover following disturbances.

中文翻译：

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珊瑚礁环礁内精细连通性的水动力驱动因素

物理和生物过程的准确表示对于解决幼虫传播途径和表征珊瑚礁生态系统的连通性至关重要。我们研究了在珊瑚属Acropora的两年一次大规模珊瑚产卵期间水动力强迫如何驱动幼虫滞留率位于澳大利亚西北部的珊瑚礁环礁（美人鱼礁）内。通过分析 41 年历史上春季和秋季珊瑚产卵事件的水动力条件，我们确定了典型和极端的水动力强迫条件。使用在珊瑚产卵期间受典型水动力条件强制的精细耦合波流水动力模型的输出进行粒子跟踪，揭示了幼虫向东穿过环礁的平均运输。运输主要由波浪和潮流共同驱动，其中残留潮汐流和单向波浪流增加了颗粒的净输出，而振荡的潮汐（非残留）流减少了珊瑚礁颗粒的净输出。然而，重要的是，由偶发性热带气旋（41 年中的 11 年）产生的极端水动力条件下的数值模拟显示，在秋季产卵期间与典型的东流有很大偏差，从而在珊瑚礁内产生了不同的连通路径。考虑到幼虫可以在珊瑚礁系统中保留相当长的时间，忽略精细的水动力过程可能会大大高估相邻珊瑚礁环礁之间的幼虫运输距离。因此，我们强调需要在区域连通性预测中考虑精细的水动力过程，这通常被认为对于理解珊瑚礁在扰动后恢复的能力并不重要。在珊瑚礁内产生不同的连接路径。考虑到幼虫可以在珊瑚礁系统中保留相当长的时间，忽略精细的水动力过程可能会大大高估相邻珊瑚礁环礁之间的幼虫运输距离。因此，我们强调需要在区域连通性预测中考虑精细的水动力过程，这通常被认为对于理解珊瑚礁在扰动后恢复的能力并不重要。在珊瑚礁内产生不同的连接路径。考虑到幼虫可以在珊瑚礁系统中保留相当长的时间，忽略精细的水动力过程可能会大大高估相邻珊瑚礁环礁之间的幼虫运输距离。因此，我们强调需要在区域连通性预测中考虑精细的水动力过程，这通常被认为对于理解珊瑚礁在扰动后恢复的能力并不重要。