Abstract

Boom-bust dynamics of invasive species have long intrigued scientists and managers alike, but quantification of such dynamics, let alone their causes, is rare. We documented the decline of a previously prolific invasive mudsnail, Batillaria attramentaria, at Elkhorn Slough estuary in central California, USA. The mudsnail was the most abundant epibenthic invertebrate in the estuary, maintaining very high densities for many decades before declining heterogeneously throughout the estuary over the past decade, decreasing in density by three orders of magnitude at some sites. We used field and laboratory experiments to test several possible mechanisms for its demise. We show that the crab Pachygrapsus crassipes can prey heavily on Batillaria. We detected high dissolution rates of Batillaria shells, and we measured greater predation rates on tethered snails with dissolved versus intact shells. Warm water temperatures and high water levels coincided with the period of most dramatic Batillaria declines (2013–2015). Localized water impoundments appear to buffer environmental drivers of the decline because Batillaria remained abundant at sites with artificial tidal restriction, while the population crashed at one site after full tidal exchange was restored. We also investigated trematode parasite prevalence and molluscicide applications to the surrounding watershed as possible causes of mudsnail declines, but they had little explanatory power. Our findings illustrate the potential for population crashes even for long-established introduced species at pest levels of abundance, and demonstrate that such declines can exhibit spatial heterogeneity. Both of these results highlight the value of investigating population dynamics of invaders across multiple temporal and spatial scales.

中文翻译：

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长期存在且异常丰富的河口中，侵入性蜗牛的空间变化和急剧下降的因素有多种

摘要

长期以来，入侵物种的繁荣与萧条动态一直引起科学家和管理人员的兴趣，但是对这种动态进行量化（更不用说其原因）的情况很少。我们在美国中部加利福尼亚州的埃尔克霍恩斯劳河口记录了以前多产的侵袭性泥螺Batillaria attramentaria的衰落。泥nail是河口中最丰富的表皮无脊椎动物，在过去的十年中，河口一直保持着很高的密度，然后在过去的十年中整个河口异质性下降，在某些地方密度下降了三个数量级。我们使用现场和实验室实验来测试其消亡的几种可能机制。我们显示螃蟹Pachygrapsus crassipes可以在Batillaria上大量捕食。我们检测到了Batillaria贝壳的溶出率很高，并且在溶解壳和完整壳的系留蜗牛上测得的捕食率更高。温暖的水温和高水位与最严重的Batillaria下降期（2013-2015年）相吻合。本地水库似乎可以缓冲环境的下降，因为巴蒂利亚（Batillaria）在受人工潮汐限制的地点，人类仍然充裕，而在完全进行潮汐交换之后，种群在一个地点坠毁。我们还研究了吸虫性寄生虫的患病率和杀软体动物剂在周围流域的应用，认为它们可能是造成泥钉下降的原因，但它们几乎没有解释力。我们的发现表明，即使是长期存在的引进物种，在有害生物数量丰富的情况下，种群崩溃的可能性也很大，并表明这种下降可能表现出空间异质性。这两个结果都凸显了调查侵略者跨多个时空尺度的种群动态的价值。