Kelp forest community resilience in action: adaptive responses of predators to a disease-driven food web perturbation

生态学的一个关键目标是了解物种相互作用——竞争、捕食、互惠——如何影响生态群落的结构（如生物多样性）和功能（如生产力），并有助于生态系统的稳定性和恢复力。北美西海岸的海带森林一直是海洋生态学家探索这些问题的模范生态系统。这项工作提供的证据表明，包括海獭、海星和鱼类在内的捕食者在控制海胆方面可能很重要，否则海胆会过度放牧森林，造成没有海带的“贫瘠”状态。然而，其他例子表明，疾病和干扰，而不是捕食者，抑制了海胆的过度放牧。在这里，我们采用实验和调查来确定海獭和海星是否以及如何单独或联合行动，以控制海胆种群的快速增长，这种增长与北美西海岸的海星“浪费”流行病同时发生。这项工作的结果将(i)促进我们对多种捕食者如何相互作用以影响群落结构，稳定性和恢复力的理解，以及（ii）阐明物种相互作用如何有助于这些森林的稳定性，这些森林是生产性商业和休闲渔业的基础。该项目将包括公民科学家参与调查海獭的数量，觅食行为和饮食，以及代表性不足（主要是拉丁裔）的本科生，结果将在几个公共宣传设施和K-12教育项目中传播。该项目将促进我们对物种多样性和捕食者在促进群落结构稳定性和弹性方面的综合作用的理解。尽管捕食者和多样性都是众多研究的焦点，但很少有人探讨捕食者多样性如何增强或不增强海洋生态系统的恢复力。研究人员将确定南部海獭（Enyhda lutris lutris）和两种海星（Pycnopodia helianthoides和Pisaster giganteus）在控制紫色海胆（strongylocentrrotus purpuratus）和蜗牛（Promartynia pulligo）两种猎物的密度和大小结构方面的相对贡献，以及对巨藻（Macrocystis pyrifera）生存和密度的级联效应。在大型野外围场/封闭环境中，捕食者通道的正交操作将用于评估两种捕食者之间的冗余、互补性和“抽样效应”（即任一物种的特别重要性）对猎物直接死亡率和间接（性状介导）觅食行为的相对作用。pi将评估实验结果是否“扩大规模”，以解释捕食者（水獭和海星）、猎物（海胆）和主要主要生产者（巨海带）相对密度的地理差异，以及海獭补偿海星数量下降的能力，以控制紫色海胆数量的快速增长，否则会导致这些生态系统的相移（森林到荒地）。

A key goal of ecology is to understand how species interactions -- competition, predation, mutualism -- influence the structure (e.g., biodiversity) and functions (e.g., productivity) of ecological communities and contribute to the stability and resilience of ecosystems. Kelp forests along the West Coast of North America have been a model ecosystem in which marine ecologists have explored these questions. That work has provided evidence that predators, including sea otters, sea stars, and fishes, can be important in controlling sea urchins that otherwise overgraze forests and create alternative "barrens" states, devoid of kelp. However, other examples suggest that disease and disturbance, not predators, suppress urchin overgrazing. Here we employ experiments and surveys to determine whether and how sea otters and sea stars act separately and in combination to control the rapid growth of sea urchin populations that is occurring in concert with a sea star "wasting" epidemic along the West Coast of North America. The results of this work will (i) advance our understanding of how multiple predators interact to influence community structure, stability and resilience, and (ii) shed light on how species interactions contribute to the stability of these forests that are the foundation of productive commercial and recreational fisheries. The project will involve citizen scientists contributing to surveys of sea otter abundance, foraging behavior and diet, and underrepresented (largely Latino) undergraduates and results will be disseminated in several public outreach facilities and K-12 educational programs. This project will advance our understanding of the combined roles of species diversity and predators in contributing to the stability and resilience of community structure. Though both predators and diversity have been the focus of numerous studies, fewer have explored how predator diversity does or does not enhance the resilience of marine ecosystems. The investigators will determine the relative contributions of southern sea otters (Enyhda lutris lutris) and two species of sea stars (Pycnopodia helianthoides and Pisaster giganteus) in controlling the density and size structure of two prey species, the purple sea urchin (Strongylocentrotus purpuratus) and a snail (Promartynia pulligo), and the cascading effects on survival and density of giant kelp (Macrocystis pyrifera). Orthogonal manipulations of predator access in large field enclosures/exclosures will be used to assess the relative roles of redundancy, complementarity and "sampling effect" (i.e. particular importance of either species) among the two predators on both direct mortality and indirect (trait-mediated) foraging behavior of their prey. The PIs will evaluate whether results from the experiments "scale up" to explain geographic variation in the relative densities of predators (otters and stars), prey (urchins) and the major primary producer (giant kelp) and the ability of sea otters to compensate for declines in sea stars to control the rapid growth in purple sea urchin populations that can otherwise cause phase shifts (forests to barrens) of these ecosystems.