Recruitment of Marine Fish Larvae to Estuarine Nursery Systems: Insights from High Resolution Analysis of Otolith Chemistry and Hydrodynamics

海洋生态学中的一个基本问题是生物和物理过程在海洋生物种群的丰度和持久性中所起的作用。虽然已经对底栖生物和潮间带生物有了一些了解，但这些因素在依赖河口的鱼类中的相对重要性尚未确定。在某种程度上，依赖河口的鱼类更难研究，因为它们经历了个体栖息地的变化。在它们的早期生活中，它们被陆上水流带过大陆架，然后到达相对狭窄的入口处，进入河口苗圃地区。然后，幼虫必须通过口腔进入河口，直到定居到适合幼体生长和生存的中盐和低盐生境。使情况更加复杂的是产卵季节的长度和许多具有经济价值的鱼类固有的产卵范围的地理宽度。对于依赖河口的鱼类来说，很难将重要性归因于任何一个因素，这在一定程度上是逻辑上的。例如，幼虫进入河口通常是间歇性的。因此，科学家只能在能够长期监测每天的幼虫供应的情况下才能检查幼虫的进入。即使如此，当产卵广泛分布时，幼虫的来源是未知的。然而，仪器和技术的改进允许一种不同的方法，对于产卵期较长的鱼类来说，这种方法在后勤上更可行。这些研究人员已经开发出量化鱼耳石(耳骨)中编码的化学特征的技术，这个特征使我们能够确定幼鱼的产卵地点和时间。此外，调查人员还可以通过随机抽样新安置的幼鱼并对其耳石切片进行化学分析来确定进入河口的日期和来源位置。这种方法为存活下来并到达育苗场的少数幼鱼提供了产卵来源和进入河口的时机。通过结合整个招募季节的这些数据，还可以生成每日幼虫进入的时间序列。当这些时间序列与河口物理过程的每日测量相关联时，调查人员可以估计产卵的时间和地点在随后通过河口和到达苗圃时的相对重要性。这项研究的时机特别适时，因为这项提议的重要杠杆将由最近由国家科学基金会内的物理海洋学项目资助的一项研究提供。这项合作研究旨在回答这样一个问题：切萨皮克湾招募的规模和时间如何取决于产卵源和近岸物理过程？这项研究的一个直接结果将是更好地了解河口近岸物理过程与幼虫供应和定居之间的联系。这些结果将为确定产卵模式，从而确定构成当地种群的鱼类来源指明方向。最后，现代渔业管理方法越来越依赖于关于招募的空间过程的知识，以确定和保护基本的鱼类栖息地，以保护不断减少的种群。这项研究将通过耳石化学追踪幼虫的传播路径，显著提高对本地种群和集合种群之间幼虫联系的了解，并将为海洋种群和保护区的管理提供关键信息。

Jones9876565A fundamental question in ocean ecology is the role that biological and physical processes play in the abundance and persistence of marine populations. Although some understanding has been gained about benthic and intertidal organisms, the relative importance of these factors has yet to be determined in estuarine-dependent fishes. In part, estuarine-dependent fishes are more difficult to study because of the ontogenic habitat shifts that they experience. During their early lives they are transported across the continental shelf by onshore currents before arriving at the comparatively narrow entrances to estuary nursery areas. Larvae must then travel through the mouth and into the estuary until settling into meso and oligohaline habitats suitable for juvenile growth and survival. Further complicating the picture are the length of the spawning season and the geographic breadth of the spawning range inherent to many of these economically valuable fishes.For estuarine-dependent fishes, the difficulty in attributing importance to any one factor has, in part, been logistic. For instance, larval entry into estuaries is typically episodic. Consequently, scientists have only been able to examine larval entry when it was possible to monitor larval supply daily over long periods. Even so, larval source was unknown when spawning was broadly distributed. However, improvement in instruments and techniques permit a different approach that is logistically more feasible for fish with broad spawning periods. These investigators have developed techniques to quantify chemical signatures encoded in the fish's otolith (earbone), a signature that allows us to determine a young fish's spawning location and time. Moreover, the investigators can determine date of entry into the estuary and source location by randomly sampling newly-settledjuveniles and chemically analyzing their sectioned otoliths. This approach provides the spawning source and timing of ingress to the estuary for the few young fish that survive and reach the nursery grounds. By combining these data throughout the recruitment season, a time series of daily larval ingress can also be generated. When these time series are correlated with daily measurements of the physical processes at an estuary mouth, the investigators can estimate the relative importance of the time and place of spawning on subsequent passage through the estuary and arrival at the nursery grounds. The timing of this study is particularly opportune, as significant leverage for this proposal will be provided by a study recently funded by the Physical Oceanography program within National Science Foundation.This collaborative research is designed to answer the question "How is the magnitude and timing of recruitment to Chesapeake Bay dependent on spawning source and nearshore physical processes?" An immediate result of the research will be a better understanding of the linkage between nearshore physical processes at an estuary mouth to larval supply and settlement. The results will point the way to identifying pattems of spawning that result in successful recruitment and therefore the sources of fish that comprise local populations. Finally, modern approaches to fisheries management increasingly rely on knowledge of spatial processes on recruitment for defining and preserving essential fish habitat to protect declining populations. This study will significantly enhance the understanding of larval connectivity among local and metapopulations by tracking larval dispersal paths via otolith chemistry and will provide critical information for the management of marine populations and reserves.