Marine Science Program, School of the Earth, Ocean, and Environment, University of South Carolina, Columbia, South Carolina, United States of America.
Department of Biology, Brigham Young University, Provo, Utah, United States of America.
PLoS One. 2018 Dec 31;13(12):e0209977. doi: 10.1371/journal.pone.0209977. eCollection 2018.
Ghost crabs have been widely used as a bio-indicator species of human impacts on sandy beaches to obtain reliable biological data for management and conservation purposes. Ghost crab population densities and individual sizes decline dramatically under human pressure. However, distribution within a beach and the factors that determine this distribution of ghost crabs is still an open question. These factors may provide valuable information for understanding human impacts on sandy beaches. Here we examine ghost crab burrows on 20 sandy beaches of South Carolina, USA under various levels of human impacts to understand the response in terms of spatial distribution of this species to human impacts. We also examine the burrow characteristics and environmental properties of the burrows to determine whether these factors alter burrow characteristics. We show that crabs on heavily impacted beaches altered their spatial distribution to mostly occupy the edges of impacted beaches. Further, this change in spatial distribution was influenced by the size distribution of the population on a beach (i.e. larger individuals occupy upper parts on the beaches). We also found that ghost crabs altered the morphology of their burrows on heavily impacted beaches. Ghost crabs create deeper, steeper and smaller burrows under human impacts. These patterns were also influenced by physical characteristics of the beach. Our results suggest that human impacts can directly influence the spatial distribution of ghost crab populations within a beach and therefore sampling at upper parts of the beaches overestimates the population density and individual sizes. Our results support the use of ghost crabs as indicator species in effective beach management, but suggest that assessments would benefit from examining the morphology and distribution of burrows as opposed to simply using burrow counts to assess the health of sandy shores.
沙蟹被广泛用作人类活动对沙滩影响的生物指示物种，以获取可靠的生物数据，用于管理和保护目的。在人类压力下，沙蟹的种群密度和个体大小会急剧下降。然而，沙蟹在海滩内的分布以及决定这种分布的因素仍然是一个悬而未决的问题。这些因素可能为了解人类对沙滩的影响提供有价值的信息。在这里，我们检查了美国南卡罗来纳州 20 个受不同程度人类影响的沙滩上的沙蟹洞穴，以了解该物种对人类影响的空间分布的反应。我们还检查了洞穴的特征和洞穴的环境特性，以确定这些因素是否改变了洞穴的特征。我们表明，受严重影响的海滩上的螃蟹改变了它们的空间分布，主要占据受影响海滩的边缘。此外，这种空间分布的变化受到海滩上种群大小分布的影响（即较大的个体占据海滩的上部）。我们还发现，受严重影响的海滩上的幽灵蟹改变了它们的洞穴形态。幽灵蟹在人类影响下会挖掘出更深、更陡峭和更小的洞穴。这些模式也受到海滩物理特征的影响。我们的结果表明，人类活动可以直接影响海滩内幽灵蟹种群的空间分布，因此在海滩上部进行采样会高估种群密度和个体大小。我们的研究结果支持将幽灵蟹用作有效的海滩管理中的指示物种，但表明评估将受益于检查洞穴的形态和分布，而不仅仅是使用洞穴数量来评估沙质海岸的健康状况。
