Fish aggregations and biogeochemical hot spots across regional environmental gradients

长期以来，海洋生态系统中的消费者在自上而下的生态系统调节中所起的作用得到了承认，但他们通过自下而上的途径（如营养供应）产生的影响往往受到低估，也没有被纳入沿海生态系统动力学模型。然而，当消费者聚集时，来自消费者的营养供应可能是一个调节因素，例如在结构复杂的栖息地周围的鱼类。研究这种自下而上的机制途径对于更全面地了解海草生态系统至关重要，海草生态系统在全球范围内都很重要且受到威胁。本研究将解决以下问题：(1)消费者集中的营养供应是否会导致海草床中不同的生物地球化学热点？(2)消费者对生态系统过程的影响在不同区域的环境背景下是如何变化的？这些项目将在加勒比海三个生物地理区域（巴哈马群岛、伊斯帕尼奥拉岛和格林纳达/圣文森特/格林纳丁斯）的多个地点进行实验。实验将利用人工珊瑚礁，模拟自然斑块珊瑚礁栖息地，高密度聚集动物。将在珊瑚礁地点测量反映生态系统过程的响应变量（例如，海草养分含量、海草生物量、主要生产者多样性），并与对照地点（没有珊瑚礁的海草地点）进行比较。生态系统过程可能受到影响的空间范围，即与人工礁的距离，将被量化并用于检测生态系统响应的生态阈值。预测变量，包括环境养分可用性，鱼类密度和鱼类放牧率的测量，将用于背景消费者介导的营养供应的相对重要性。分层实验设计和双管齐下的分析将描述在生物地理区域之间和内部发现的环境梯度之间的关系，促进预测何时、何地以及为什么消费者介导的营养供应是海草床生态系统过程的重要控制所需的概念框架。更广泛的影响：该项目旨在通过广泛整合研究和教育工作，在地区、国家和地方各级发挥更广泛的影响。整个项目是与大自然保护协会合作设计的，PI是该协会的加勒比顾问委员会成员。大自然保护协会是“加勒比挑战”的先锋，致力于到2020年保护20%的海洋栖息地。作为加勒比挑战计划的一部分，所有计划中的研究地点都是当前或拟议的海洋保护区的一部分。这项研究的数据将为监测计划、管理策略和保护措施的优先次序提供信息。地方和国家一级的外联倡议将考虑到当地的环境和社会机会和挑战。例如，在巴哈马，PI将帮助在阿巴科岛上设计和开发一个新的中心，旨在支持研究、教育和保护活动：ACRE（阿巴科保护、研究和教育中心）。外联网站“阿巴科科学家”将得到扩大，继续提供一个向公众快速传播信息的平台。重点将放在培训在科学领域代表性不足的少数民族学生，在综合科学、教育和跨文化整合模式中提供经验。

Consumers in marine ecosystems have long been acknowledged for their role in top-down regulation of ecosystems, but their influence through bottom-up pathways such as nutrient supply is often underappreciated and has not been integrated into models of coastal ecosystem dynamics. Yet, nutrient supply from consumers may be a regulating factor when consumers aggregate, such as fishes around structurally complex habitat. Examining this bottom-up mechanistic pathway is essential for a more holistic understanding of seagrass ecosystems, which are important and threatened globally. This study will address the following questions: (1) Does concentrated nutrient supply from consumers result in distinct biogeochemical hot spots in seagrass beds? and (2) How do consumer effects on ecosystem processes vary across regional environmental contexts where nutrient availability and fishing pressure vary? The PIs will conduct experiments at multiple sites within three biogeographic regions in the Caribbean (The Bahamas, Hispaniola, and Grenada/St.Vincent/Grenadines). The experiments will utilize artificial reefs that mimic natural patch reef habitats that concentrate animals at high densities. Response variables reflecting ecosystem processes (e.g., seagrass nutrient content, seagrass biomass, primary producer diversity) will be measured at reef sites and compared with control sites (seagrass sites without reefs). The spatial extent over which ecosystem processes may be affected, i.e., distance from artificial reef, will be quantified and used to detect ecological thresholds in ecosystem responses. Predictor variables, including measures of ambient nutrient availability, fish densities and fish grazing rates, will be used to contextualize the relative importance of consumer-mediated nutrient supply. The hierarchical experimental design and two-pronged analysis will characterize relationships across environmental gradients found among and within the biogeographic regions, facilitating a conceptual framework needed to predict when, where, and why consumer-mediated nutrient supply is an important control of ecosystems processes in seagrass beds. Broader Impacts: The project is designed to maximize broader impacts at regional, national, and local levels through extensive integration of research and education efforts. The entire program is designed in partnership with The Nature Conservancy, for which the PI serves on the Caribbean Advisory Board. The Nature Conservancy is at the forefront of the Caribbean Challenge, an effort to protect 20% of marine habitats by the year 2020. All of the planned study sites are part of current, or proposed, marine protected areas as part of the Caribbean Challenge initiative. Data from the research will inform monitoring plans, management strategies, and prioritization of conservation measures. Outreach initiatives at local and national levels will be designed with sensitivity to local environmental and social opportunities and challenges. For example, in The Bahamas, the PI will help design and develop a new center on Abaco Island intended to support research, education and conservation activities: ACRE (the Abaco Conservation, Research & Education Center). The outreach website "The Abaco Scientist" will be expanded, continuing to provide a platform for quick dissemination of information to the general public. Emphasis will be placed on training minority students under-represented in the sciences, providing experiences within an integrated science, education, and cross-cultural integration model.