Collaborative Research: Hydrographic Change and Effects on Bivalve Communities and Top Avian Consumers in the Bering Sea

该项目将研究海洋变化是否导致双壳类群落的长期变化，从而导致世界镜贝种群的能量和生存。镜贝是一种潜水海鸭，冬季以圣劳伦斯岛波利尼亚(SLIP)附近的底栖无脊椎动物为食。该项目有四个目标：1)对过去25-50年收集的主要双壳类的种类和大小结构进行回顾分析，以及对每年一个周期收集的样本进行类似的分析；2)研究物理/生物水文过程指标(沉积物吸氧率、颗粒大小和碳含量)的最新变化；3)调查对双壳类生产的其他影响(冰盖、海流输送、生产力、海象/海星捕食)；以及4)建立模拟模型，将双壳类被捕食的特征与双壳类的能量收支联系起来。以往的研究表明，滑移和阿纳德尔湾(GOA)冷池对底栖动物群落结构和生物量有重要影响。自1988年以来在5-8月夏季对圣劳伦斯岛南部进行的海洋学研究表明，由于水文动力增强了近岸初级生产力，以及随后富含颗粒有机碳的水域从该岛向西南方向输送，维持了非常高的底栖动物现存量(高达45g Cm-2)。1995年3月，在海冰高度集中的圣劳伦斯岛南部，第一次发现了多达300,000只有镜面斑羚的大群。1996年和1997年的调查证实，滑道下游的这一地区是实际上全世界镜羚种群的主要越冬地点。虽然作为越冬策略，这些鸟类底栖动物会潜入40-60米深的亚冰水中越冬，这似乎令人惊讶，但先前的研究表明，该地区出现了非常大密度的小型双壳类(Nucula belloti和Nuculana Radiata，1-3厘米长)。每一种双壳类对特定的沉积物粒度都有偏好，因此改变沉积模式和碳负荷可能会对双壳类种群结构产生很大影响。在过去的25年里，白鹭的数量急剧下降，历史数据表明，圣劳伦斯岛南部的优势双壳类群落在这一时期也发生了变化。滑移中结冰强度的可能变化，以及影响果阿冷池的运输条件的相关变化，可能影响了双壳类的种类和大小结构。模拟模型表明，这些猎物的特征强烈地影响着羽毛的能量收支。因此，eiders可能是气候调节的冰、水文、远洋生物和底栖动物之间的相互作用如何影响上层营养水平的关键指标。这个项目将描述和分析北极底栖生物系统中这些相互作用的强度。这个项目将与一个已经资助的、为期一年的物理海洋学项目相互作用。物理海洋学计划将于1998年9月在圣劳伦斯岛以南部署一系列系泊设施，以研究运输条件。与这一水文计划的合作将大大加强对1998年秋季、1999年冬末和1999年夏季进行的生物和沉积物测量的解释。这种合作还包括与使用合成孔径雷达卫星图像实时研究海冰动力学的科学家进行互动。合作的最终结果将是对物理强迫功能(水文、冰)和营养过程(底栖到顶端捕食者)之间的相互作用进行评估。这将允许模拟羽毛能量学和种群对不同冰条件和不同气候情景下底层底栖群落变化的敏感度。

This project will examine whether oceanographic changes have resulted in long-term shifts in bivalve communities and thus the energetics and survival of the world population of Spectacled Eiders, a diving seaduck that feeds on benthic invertebrates near the St. Lawrence Island Polynya (SLIP) during winter. The project has four objectives: 1) retrospective analyses of the species and size structure of dominant bivalves collected over the past 25-50 years, along with similar analyses of samples to be collected over an annual cycle, 2) studies of recent changes in indicators of physical/biological hydrographic processes (sediment oxygen uptake rates, grain size, and carbon content), 3) investigation of alternative influences on bivalve production (ice cover, current transport, productivity, walrus/sea star predation), and 4) simulation modeling to relate bivalve prey characteristics to eider energy budgets. Previous studies indicate that the SLIP and Gulf of Anadyr (GOA) cold pool have an important influence on benthic community structure and biomass. Oceanographic studies south of St. Lawrence Island conducted in the May-August summer season since 1988 show that very high standing stocks of benthic infauna (up to 45 g C m-2) are maintained by nearshore primary production enhanced by hydrographic dynamics, and subsequent transport of waters rich in particulate organic carbon southwestward from the island. In March 1995, large flocks of up to 300,000 Spectacled Eiders were located for the first time south of St. Lawrence Island amid high concentrations of sea ice. Surveys in 1996 and 1997 confirmed that this area downstream of the SLIP is the major overwintering site for virtually the entire world populations of Spectacled Eiders. While it may seem surprising that these avian benthivores would dive in 40-60 m of sub-freezing water in ephemeral leads in the shifting pack ice as an overwintering strategy, prior studies showed that very large densities of small bivalves occur in this region (Nucula belloti and Nuculana radiata, 1-3 cm long). Each bivalve species has a preference for a specific sediment grain size, so changing sedimentation patterns and carbon loading may greatly impact bivalve population structure. Spectacled Eider populations have declined dramatically in the last 25 years, and historical data suggest that dominant bivalve communities south of St. Lawrence Island have also changed during this period. Possible alterations in the intensity of ice formation in the SLIP, and associated changes in transport conditions affecting the GOA cold pool, might have affected the species and size structure of bivalves. Simulation models suggest that these prey characteristics strongly influence eider energy budgets. Thus, eiders may be key indicators of how climate-mediated interactions between ice, hydrography, pelagic production, and benthos affect upper trophic levels. This project will characterize and analyze the strength of these interactions in an Arctic benthic system.This project will interact with an already funded, yearlong physical oceanographic program. The physical oceanographic program will deploy an array of moorings south of St. Lawrence Island in September 1998 to study transport conditions. Cooperation with this hydrographic program will greatly enhance interpretation of the biological and sediment measurements to be made in fall 1998, late winter 1999, and summer 1999. This collaboration also involves interaction with scientists investigating sea ice dynamics using SAR satellite imagery in a real-time manner. The end result of the collaborations will be evaluation of the interactions between physical forcing functions (hydrographic, ice) and trophic processes (benthic to top predators). This will allow simulation of eider energetics and population sensitivity to varying ice conditions and changes in underlying benthic communities under different climate scenarios.