Collaborative Research: Cobble landscape structure, spatial gradients in predation, and variable demographic bottlenecks in the American lobster

了解定居前和定居后过程如何相互作用以控制海洋开放种群的动态，仍然是海洋生态学的一个中心问题。在这项研究中，美国龙虾Homarus americanus被用作一个模式系统，以确定托儿所的栖息地结构如何影响定居后的死亡率和扩散。这项研究的中心主题是找出新英格兰海岸线上鹅卵石景观结构(即斑块)和龙虾种群密度、捕食者丰度和捕食者多样性的梯度是否相互作用，导致假设的龙虾幼体种群瓶颈强度的区域差异。当幼年龙虾到达紧急阶段时，它们必须在鹅卵石庇护所之外觅食，即使它们还没有达到躲避捕食者(例如底层鱼)的大小庇护所，它们也可能成为庇护所有限的动物。基本的假设是，鹅卵石斑块和庇护所的限制将导致人口瓶颈，限制捕食者密度高的地区(如新英格兰南部)的龙虾数量，但不限制捕食者密度低的地区(如缅因州)的龙虾数量。美国国家科学基金会资助的这项研究补充了新英格兰海岸十多年来由国家支持的幼体后定居调查，以及NOAA支持的侧扫声纳、远程车辆和潜水调查，以评估龙虾丰度和栖息地使用之间的区域联系，并用鹅卵石栖息地结构和定居强度指数来补充调查。这些指标旨在确定是否存在以下方面的区域差异：(1)龙虾在栖息地之间的移动；(2)捕食风险；(3)当地避难所的限制；以及4)避难所的保真度(更换避难所的倾向)。在四个地区(罗德岛、马萨诸塞州、中海岸和缅因州东部)的两个地点中的每个地点，调查人员将构建由一个碎裂的和一个非碎裂的鹅卵石斑块阵列组成的实验景观。在这些景观中，幼年龙虾从被放生的源地迁移到周围目的地地块的比例将与阵列类型、捕食者丰度、捕食风险和龙虾种群密度相关联，以推断在龙虾栖息地损失中扩散和死亡的相对贡献。在另一项实验中，将部署人工避难所的大小阵列，以量化按地区划分的特定大小避难所的限制程度。将进行相应的捕食实验，以确定捕食的脆弱性在区域上是如何变化的。龙虾的大小既受到当地庇护所的限制，又仍然容易受到捕食的影响，这将表明幼体受到人口瓶颈的影响。最后，他们将标记龙虾以衡量避难所的保真度，以确定避难所之间的活动如何与龙虾密度、捕食者指数或地点之间的栖息地斑块相关。这些综合项目的结果将广泛传播。美国龙虾是新英格兰最重要的单品种渔业。通过解决龙虾定居后过程的黑匣子，这些科学家将为长期存在的科学愿景做出贡献，即开发一个大规模的空间显式模型，将远洋过程和海底过程结合起来，预测空间和时间上的收获。它们的结果将有助于资源管理人员和渔业继续开发渔业预测工具。学生培训也是这项工作不可或缺的一部分：拟议的研究将成为SDSU研究生论文或论文的基础，每年至少有四名本科生作为获得学术学分的实习生。该项目的另一个重要教育组成部分是继续开发一种名为Hatch-to-Catch的互动光盘和基于网络的活动，该活动已被国家科学教师协会确认为K-12学习的有用教育工具(见www.scilinks.org)。

Understanding how pre- and post-settlement processes interact to govern the dynamics of marine open populations remains a central issue in marine ecology. In this study the American lobster Homarus americanus is used as a model system to determine how nursery habitat structure influences post-settlement mortality and dispersal. The central theme of the study is to find if cobble landscape structure (i.e., patchiness) and gradients in lobster population density, predator abundance and predator diversity along the New England coastline interact to cause regional variation in the strength of a hypothesized juvenile lobster demographic bottleneck. As juvenile lobsters reach the emergent phase they must forage outside of cobble shelter and may become shelter limited even though they have not reached a size refuge from predators (e.g., groundfish). The underlying hypothesis is that cobble patchiness and shelter limitation will cause a demographic bottleneck that limits lobster abundance in regions of high predator density (e.g., southern New England) but not in regions of low predator density (e.g., Maine). Supplementing more than a decade of state-supported postlarval settlement surveys along the New England coast, and NOAA-supported sidescan sonar, remote vehicle and scuba surveys to evaluate the regional linkage between lobster abundance and habitat use with indices of cobble habitat structure and settlement strength this NSF-sponsored research will complement the surveys with manipulative experiments. These are aimed at determining if regional differences exist in: (1) lobster movements among habitat patches; (2) predation risk; (3) local shelter limitation; and 4) shelter fidelity (propensity to switch shelters). In each of two sites in four regions (Rhode Island, Massachusetts, mid-coast and eastern Maine) the investigators will construct experimental landscapes consisting of one fragmented and one non-fragmented cobble patch array. The proportion of juvenile lobsters moving from a source patch where they are released to surrounding destination patches within these landscapes will be correlated with array type, predator abundance, predation risk, and lobster population density to infer the relative contributions of dispersal and mortality in lobster losses from settlement patches. In a separate experiment, size arrays of artificial shelters will be deployed to quantify the degree of size-specific shelter limitation by region. Corresponding predation experiments will be conducted to determine how vulnerability to predation varies regionally. The lobster size that is both locally shelter-limited and still vulnerable to predation will indicate the size at which juveniles are subject to a demographic bottleneck. Finally, they will tag lobsters to measure shelter fidelity to determine how movements between shelters correlates with lobster density, predator indices, or habitat patchiness among sites. Results of these integrated projects will be broadly disseminated. The American lobster is the most economically important single-species fishery in New England. By addressing the black box of lobster post-settlement processes, these scientists will contribute to a long-standing scientific vision of developing a large-scale spatially explicit model that couples pelagic and benthic processes to predict harvests in space and time. Their results will aid resource managers and the fishing industry in the continued development of predictive tools for the fishery. Student training is also integral to this work: the proposed research will form the basis for a thesis or dissertation for an SDSU graduate student, and at least four undergraduates per year will serve as interns earning academic credit. Another important educational component of this project is the continued development of an interactive CD and web-based activity called Hatch-to-Catch already recognized by the National Science Teachers Association as a useful educational tool for K-12 learning (see www.scilinks.org).