Global analysis of stratification impacts on seabirds through food resources

全球变暖正在通过改变海洋栖息地来影响世界海洋，但对海洋生物的影响因海洋区域而异。可能解释这些观测结果的一个因素是，海洋表面水域变暖的速度快于深层水域。温差可能会成为混合的物理屏障，从而阻碍更深层次的营养物质到达阳光充足的表面，在那里它们被海洋植物用于光合作用。随着混合的减少，海洋上层的生产力可能会降低，这反过来可能会影响对社会具有经济和文化(生态)价值的海鱼、鸟类和哺乳动物种群。为了进行这项研究，研究人员正在利用现有的长期数据，研究海洋变暖对浮游生物、小鱼数量和世界各地海鸟繁殖成功的影响。他们正在建立数学关系，以了解不同深度的海洋变暖如何与浮游生物、鱼类和鸟类的生产力有关。结果将为选择哪些海鸟物种可能最适合作为全球不同生态系统变化的生态指标提供关键信息，因此对远程海洋监测具有影响。该项目将为即将发布的联合国评估报告贡献新的科学理解，并通过以海雀和企鹅等受欢迎的海鸟为中心的宣传材料，提高公众对海洋健康的认识。它将支持早期职业和博士后科学家。海洋热层结是决定世界海洋上层带初级生产力的一个重要因素。最近的一项全球分析显示，在上层带觅食的食鱼海鸟的繁殖生产力呈下降趋势，但层化程度的增加仍有待作为解释因素进行调查。该项目的主要目标是检验这样一种假设，即海鸟物种群体通过层化对上层食物资源的可获得性和/或鸟类对猎物的利用的间接影响，对不断增加的温度层化作出不同的反应。研究人员正在验证这样一种预测，即温度层结对捕食性地表觅食物种的繁殖生产力影响最大。他们正在将一个关于海鸟生产力的新的全球数据库与欧洲格洛里斯模型提供的关于热层结的高分辨率数据以及来自NASA的卫星叶绿素a数据相结合。他们正在使用广义线性混合模型来测试海鸟群体之间的差异，并使用结构方程模型来测试从分层到猎物可获得性对海鸟生产力的直接和间接反应路径，重点是横跨南北半球海洋盆地的中高纬度生态系统。结果将增进对海鸟如何应对日益增加的热层积与海鸟生活史特征的根本差异的理解。回溯性分析将促进人们对以不同猎物为食的海鸟以及世界海洋不同表层栖息地的海鸟如何应对最近层化的反应的了解。更广泛地说，这项研究将有助于洞察上层海洋的物理变化如何通过食物资源的可用性影响捕食者。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Global warming is affecting the world’s oceans by altering marine habitats, yet the effects on marine life vary by ocean region. One factor that may explain these observations is that ocean surface waters have warmed faster than deeper waters. Temperature differences may act as a physical barrier to mixing, thereby impeding deeper nutrients from reaching the sunlit surface where they are used by ocean plants in photosynthesis. With less mixing, the upper layers of the ocean may have become less productive, which may in turn impact marine fish, bird, and mammal populations of economic and cultural (ecological) value to society. To conduct this study, the investigators are examining the effects of ocean warming by depth on the abundance of plankton, small fish, and the breeding success of marine birds across the world using existing long-term data. They are developing mathematical relationships to understand how ocean warming at various depths is linked to plankton, fish, and bird productivity. Results will provide key information for selecting which seabird species may be best suited as ecological indicators of change for different ecosystems across the globe, and therefore has implications for remote-ocean monitoring. The project will contribute new scientific understanding for upcoming United Nation assessment reports and enhance public awareness of ocean health through outreach materials centered on popular seabirds such as puffins and penguins. It will support early career and postdoctoral scientists.Ocean thermal stratification is an important factor determining primary productivity in epipelagic zones of the world’s oceans. A recent global analysis showed declining trends in the breeding productivity of fish-eating seabirds that forage in the epipelagic zone, but increasing stratification has yet to be investigated as an explanatory factor. The primary objective of this project is to test the hypothesis that seabird species groups vary in their responses to increasing thermal stratification through the indirect effects of stratification on epipelagic food resource availability and/or prey use by the birds. The investigators are testing the prediction that thermal stratification has the largest effect on breeding productivity of piscivorous, surface-foraging species. They are integrating a new global database on seabird productivity with high-resolution data on thermal stratification available from the European GLORYS model, as well as satellite-based chlorophyll-a data from NASA. They are using Generalized Linear Mixed Models to test for variation between seabird groups and Structural Equation Models to test direct and indirect pathways of response from stratification through prey availability to seabird productivity, focusing on mid-to-high latitude ecosystems across ocean basins in both the northern and southern hemispheres. Results will improve understanding of how seabirds respond to increasing thermal stratification in relation to fundamental differences in seabird life history traits. The retrospective analysis will advance knowledge of how seabirds that feed on different prey, and in different epipelagic habitats of the world’s oceans, have responded to recent increases in stratification. More generally, the study will contribute insight into how physical changes in the upper ocean affect predators through the availability of food resources.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.