Are blue crab declines leading to a trophic cascade and massive loss of U.S. southern marshes?

蓝蟹的减少是否会导致营养级联反应和美国南部沼泽地的大量损失？

• 批准号: 1439504
• 负责人: Brian Silliman
• 金额: $ 0.84万
• 依托单位: Duke University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-01-15 至 2014-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1439504&HistoricalAwards=false
• 关键词: blue; crab; declines; leading; trophic

A fundamental goal of ecology is to understand the physical and biological processes that control plant production and distribution patterns in natural communities. For over 6 decades, salt marsh plant assemblages have been considered a classic example of a bottom-up regulated community dominated by relatively unpalatable plants controlled by physical conditions and nutrient supplies. Recent research in southeastern U.S. salt marshes, however, challenges this paradigm and suggests that powerful trophic interactions are equally important mechanisms. In Virginia, Louisiana, and Georgia salt marshes, the PI found that the common marsh snail, Littoraria, is capable of exerting strong, top-down control of marsh plants. Unless kept in check by its predators, this snail can transform a highly productive ecosystem to barren mudflat.Over the past decade, large expanses of southeastern U.S. salt marshes (100's of km2) have experienced unprecedented die-back. From 2002-2006, surveys of 20 die-off areas revealed snail densities exceeding 1000/m2 on die-off borders. In exclusion experiments in GA, FL and LA, snails actively converted salt marshes to barren mudflats. These findings and the concurrent, steep decline (20-80%) of blue crab densities over the past decade suggest that cascading consumer effects discovered in small-scale experiments may apply to a larger trophic cascade that contributes to die-off in southern salt marshes. There have, however, been no studies of how commercially important blue crabs regulate marsh die-off via suppression of snail densities. This knowledge gap will be address with the following questions:1) What is the role of blue crabs in regulating snail populations? This question will be evaluate with multi-site experiments of both blue crab inclusions and exclusions.2) Does spatial variation in blue crab densities across marsh landscapes determine spatial variation in predation, subsequent grazer outbreaks, and marsh die-off in areas of low crab density? To evaluate this question, broad-scale surveys (20 sites) will identify relationships among blue crab and snail density, grazing intensity and plant biomass.3) Have blue crab population declines indirectly contributed to marsh die-off by releasing plant-grazing snails from top-down control in recent history? This question will be evaluated using a correlative approach, with long-term (~30 yrs) data (FWS, LTER) sets of blue crab harvests, snail densities, and incidence of scarring on archived snail shells.Intellectual Merit: This research would contribute a new, top-down mechanism for control of salt marshes, and reveal if blue crabs are keystone predators in the trophic cascade. Evidence for species-specific, higher trophic level control of plant growth and recent community die-off would compel ecologists to reevaluate the 60-yr-old bottom-up paradigm in salt marsh ecology.Broader Impacts: The consequences of marsh die-off are far-reaching for humans, since marsh grasses provide many essential services (e.g., shoreline protection). Results from this proposed research would allow managers to predict effects of predator (i.e., blue crabs) depletion and to formulate effective strategies for marsh conservation (e.g. reduced fishing). To facilitate inter-stake-holder-communication on the role of consumers in marsh die-off, results will be presented in a series of seminars and Q&A sessions to key stakeholders: the public, fishermen, and marsh managers (TNC, FWS). In addition, educational, outreach activities, in collaboration with high school teachers, will engage students that are excelling (boy scouts) and at-risk (low grades/attendance) in hands-on field science and potential career opportunities through: 1) field classes, 2) research and 3) a marine symposium (e.g., as previously at UF 2008).

生态学的一个基本目标是了解控制自然群落中植物生产和分布模式的物理和生物过程。 60多年来，盐沼植物群落一直被认为是一个典型的例子，一个自下而上的调节社区占主导地位的相对不好吃的植物控制的物理条件和营养供应。 然而，最近在美国东南部盐沼的研究挑战了这种范式，并表明强大的营养相互作用同样重要的机制。 在弗吉尼亚、路易斯安那和格鲁吉亚的盐沼中，PI发现普通的沼泽蜗牛Littoraria能够对沼泽植物施加强大的自上而下的控制。 除非受到捕食者的控制，这种蜗牛可以把一个高产的生态系统变成贫瘠的泥滩。在过去的十年里，美国东南部大片的盐沼（100平方公里）经历了前所未有的枯死。 2002-2006年，对20个灭螺区的调查显示，在灭螺区边界，钉螺密度超过1000只/m2。 在GA，FL和LA的排斥实验中，蜗牛积极地将盐沼转化为贫瘠的泥滩。 这些发现以及在过去十年中蓝蟹密度的急剧下降（20-80%）表明，在小规模实验中发现的级联消费者效应可能适用于导致南部盐沼死亡的更大的营养级联。 然而，还没有研究如何商业上重要的蓝蟹调节沼泽死亡通过抑制蜗牛密度。 这个知识缺口将通过以下问题来解决：1）蓝蟹在调节蜗牛种群中的作用是什么？ 这个问题将进行评估与多站点实验的蓝蟹夹杂物和排除。2）在整个沼泽景观蓝蟹密度的空间变化确定捕食的空间变化，随后的食草动物爆发，和沼泽死亡关闭在低螃蟹密度的地区？ 为了评估这个问题，大规模的调查（20个站点）将确定蓝蟹和蜗牛密度，放牧强度和植物生物量之间的关系。3）蓝蟹种群下降间接导致沼泽死亡关闭释放植物放牧蜗牛自上而下的控制在最近的历史？ 这个问题将使用相关的方法进行评估，与长期（~30年）的数据（FWS，LTER）集的蓝蟹收成，蜗牛密度，和存档的蜗牛shells.Intellectual优点疤痕的发病率：这项研究将有助于一个新的，自上而下的机制控制盐沼，并揭示如果蓝蟹是关键的捕食者在营养级联。 物种特异性的证据，植物生长的更高营养级控制和最近的群落死亡将迫使生态学家重新评估60岁的自下而上的范式在盐沼生态学。更广泛的影响：沼泽死亡的后果是深远的人类，因为沼泽草提供了许多重要的服务（例如，海岸线保护）。 这项研究的结果将使管理者能够预测捕食者的影响（即，（例如，减少蓝蟹）枯竭，并制定有效的沼泽保护战略（例如，减少捕鱼）。 为了促进利益相关者之间就消费者在沼泽消亡中的作用进行沟通，将在一系列研讨会和问答会上向主要利益相关者介绍结果：公众、渔民和沼泽管理者（TNC、FWS）。 此外，教育，推广活动，与高中教师合作，将通过以下方式吸引优秀（童子军）和风险（低年级/出勤率）的学生参与实地科学实践和潜在的职业机会：1）实地课程，2）研究和3）海洋研讨会（例如，2008年以前的UF）。