Moving From Sea to Land Via the Freshwater Route: Larval Physiology and Mode of Recruitment in a Freshwater Fiddler Crab

在这项研究中，我们将开发一种分子方法来识别美国东南部盐沼群落中常见的三种招潮蟹物种的神秘幼虫形式。虽然这些密切相关的物种（Uca minax、Uca pugnax 和 Uca pugilator）的成虫是研究最多的盐沼无脊椎动物之一，但对幼蟹和幼蟹的研究却受到阻碍，因为它们在早期生命阶段在形态上无法区分。使用快速、廉价的分子测定，我们将绘制这三个物种的分布图，从春末开始，当它们在开放的沿海水域完成幼体发育后开始进入南卡罗来纳州北湾河口的河口，直到深秋，当年最后的幼体加入成熟的成年种群。 根据这些信息，我们将制作 Uca 蟹每年入侵沼泽的高分辨率模型。我们将确定这三个物种的幼体进入其成年同类优先占据的栖息地的时间、位置和程度。我们将了解这三个物种的迁徙是否不同，或者它们的幼崽是否平等地渗透到所有区域，以及定居后不同的死亡率决定了河口内成虫的分布。现场的估计将通过实验室实验进行完善，在实验室实验中，这三个物种的幼蟹将在低或高盐度条件下暴露于成虫栖息地的沉积物中。幼蟹对这些环境信号的反应可能解释了它们定位成年蟹栖息地的能力。这项研究的更广泛影响在于我们正在开发的分子测定法，以区分这三种螃蟹的幼蟹。招潮蟹通过改变其挖洞和进食区域的物种组成、景观地形和水化学，对东南河口产生了严重影响。此外，成年螃蟹占湿地鸟类饮食的很大一部分，而螃蟹幼虫是小鱼的重要猎物，而商业和游钓渔业中的大型鱼类则以这些小鱼为食。我们的测定将使我们能够评估沼泽生态系统随时间的稳定性，并将有助于估计甲壳类动物的生物多样性。这项检测的发展将让我们首次详细研究这些被广泛研究的螃蟹的整个生命周期，从而消除我们理解盐沼中的出生、补充和死亡的一大障碍。

In this study, we will develop a molecular method to identify the cryptic larval forms of three fiddler crab species common in salt marsh communities of the southeastern United States. While the adults of these closely related species, Uca minax, Uca pugnax, and Uca pugilator, are among the most studied of salt marsh invertebrates, work on larval and juvenile crabs has been hindered because they are morphologically indistinguishable at these early life stages. Using a fast, inexpensive molecular assay, we will map the distribution of these three species starting in late spring when they begin to enter the mouth of South Carolina's North Inlet estuary after completing larval development in open coastal waters until late fall when the last of the year's young have joined the established adult populations. From this information, we will produce a high-resolution model of the annual invasion of the marsh by Uca crabs. We will determine the timing, position, and degree of penetration by young of the three species into habitats preferentially occupied by their adult counterparts. We will learn if the three species migrate differently, or if their young penetrate all areas equally and differential mortality after settlement determines adult distributions within the estuary. Estimates from the field will be refined with lab-based experiments in which young crabs of the three species will be exposed to sediment from adult habitats under low or high salinity conditions. How young crabs respond to these environmental cues may explain their ability to locate adult habitats.The broader impact of this study lies in the molecular assay that we are developing to differentiate young of these three crab species. Fiddler crabs heavily impact southeastern estuaries by modifying species composition, landscape topography, and water chemistry in areas where they burrow and feed. Also, adult crabs can comprise a large portion of the diets of wetland birds and crab larvae are important prey for small fishes that are eaten by larger fishes exploited by commercial and sport fisheries. Our assay will allow us to assess the stability of marsh ecosystems over time and will be useful in estimating crustacean biodiversity. The development of this assay will eliminate a large hurdle in our understanding of birth, recruitment, and death in the salt marsh by allowing us to investigate the full life cycles of these widely studied crabs in detail for the first time.