SGER: Food Web Structure Across a Large-scale Ocean Productivity Gradient: Top Predator Assemblages in the Southern Indian Ocean

生物海洋学的一个普遍目标是了解构成远洋群落的过程。过去的研究表明，海洋物种分布在各种时空尺度上受到物理和生物变异的影响。本研究的目的是验证上层捕食者的分布和群落变化与上层生态系统的物理结构和海洋生产力的大尺度变化一致的假设。为了验证这一假设，将对南印度洋不同海洋领域的海洋鸟类和哺乳动物进行跨学科调查。这项探索性研究小额赠款将为两名美国科学家提供机会，让他们登上留尼旺岛附近的一艘法国科考船。法国科学家将对自然环境进行采样，并估计海洋生产力，而美国科学家将调查从亚热带到亚南极水域在35度纬度梯度上的物理和生物特性的顶级捕食者分布。要解决的主要假设是，顶级捕食者的组合是由水文特性和海洋生产力模式的空间梯度构成的，这些特征和模式已知会影响浮游动物、鱼类和鱿鱼猎物的分布和斑块。据推测，在一个特定的海洋区域内，海洋顶级捕食者的总体丰度在很大程度上取决于海洋生产力。此外，据推测，觅食的能量成本决定了哪种类型的海洋顶级捕食者栖息在特定的海洋区域。具有高觅食成本的物种被限制在高产区内密集的猎物聚集。相反，觅食成本低的类群能够生活在低生产力地区，在那里它们利用更分散的猎物资源。为了验证这些假设，我们将量化顶级捕食者组合与特定水质量的空间关联，以及顶级捕食者的流速和水深域的总体反应。由于顶级捕食者在多个时间和空间尺度上对海洋变异性做出反应，我们将在两个特定的空间尺度上评估它们对栖息地变异性的反应。研究将使用多种分析方法，包括粗尺度生境偏好的成分分析、广义加性模型、循环类群分析、水文数据和顶部捕食者组合的排序以及顶部捕食者聚集的测量。该研究将在亚热带和亚南极印度洋大尺度（1000公里）和大尺度（10公里）水文和海洋生产力模式的背景下研究中上层食物网的空间变异性。这种跨学科的观点将增强我们对南印度洋中上层生物群落结构的物理和生物过程的理解，并将提供一个对整个海洋具有更广泛影响的模型。

A pervasive goal of biological oceanography has been to understand the processes that structure pelagic communities. Past research suggests that oceanic species distributions are influence by physical and biological variability at a variety of spatial-temporal scales. The objective of this research is to test the hypothesis that the dispersion and community of top predators vary in concordance with large-scale variability in physical structure and ocean productivity in pelagic ecosystems. To test this hypothesis, an inter-disciplinary survey of marine bird and mammal use of distinct oceanographic domains in the Southern Indian Ocean will be conducted. This Small Grant for Exploratory Research will provide the opportunity to place two U.S. scientists on board a French research vessel near Reunion Island. The French scientists will sample the physical environment and estimate oceanic productivity while the U.S. scientists will survey top predator distributions across a 35 degree latitudinal gradient in physical and biological properties from subtropical to sub Antarctic waters. The primary hypothesis to be addressed is that top predator assemblages are structured by spatial gradients in hydrographic properties and ocean productivity patterns known to influence the distribution and patchiness of their zooplankton, fish and squid prey. It is hypothesized that the overall abundance of marine top predators within a specific oceanic domain is largely determined by ocean productivity. Also, it is hypothesized that the energetic costs of foraging determine which types of marine top predators inhabit specific oceanic domains. Species with high foraging costs are constrained to exploit dense prey aggregations within highly productive areas. Conversely, taxa with low foraging costs are able to inhabit low productivity areas, where they exploit more dispersed prey resources.To test these hypotheses, we will quantify the spatial association of top predatorassemblages with specific water masses and the aggregative response of top predators athydrographic and bathymetric domains. Because top predators respond to oceanographicvariability at multiple scales of time and space, we will assess their responses tohabitat variability at two specific spatial scales. A variety analytical methods will be used, including compositional analysis of coarse-scale habitat preferences, generalized additive models, recurrent group analysis, ordination of hydrographic data and top predator assemblages and the measurement of top predator aggregation. The research will address spatial variability in pelagic food webs within the context of large (1000s km) and coarse (10s km) scale hydrographic and ocean productivity patterns in the subtropical and sub Antarctic Indian Ocean. This inter-disciplinary perspective will enhance our understanding of the way physical and biological processes structure pelagic communities in the southern Indian Ocean and will provide a model that has broader implications for the oceans as a whole.