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了双壳类动物群落的长期变化，从而影响了眼镜鸭的能量和世界种群的生存。眼镜鸭是一种潜水海鸭，在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年收集的优势双壳类的种类和大小结构进行回顾性分析，并对每年收集的样本进行类似分析；2)研究物理/生物水文过程指标（沉积物吸氧率、粒度和碳含量）的近期变化；3)调查对双壳类生产的其他影响（冰盖、洋流运输、生产力、海象/海星捕食）；4)建立双壳类猎物特征与羽绒动物能量收支关系的仿真模型。以往的研究表明，SLIP和GOA湾冷池对底栖生物群落结构和生物量有重要影响。自1988年以来，在圣劳伦斯岛南部的5 - 8月夏季进行的海洋学研究表明，近岸初级生产在水文动力学的促进下，以及随后从该岛向西南方向输送的富含颗粒有机碳的水，维持了非常高的底栖动物存量（高达45 g C - m2）。1995年3月，在圣劳伦斯岛以南高度集中的海冰中，首次发现了多达30万只的大群眼镜羽鸭。1996年和1997年的调查证实，SLIP下游的这一地区实际上是世界上所有眼镜绒鸭种群的主要越冬地点。虽然这些底栖鸟类会潜入40-60米的低于冰点的水中，在浮冰的短暂流动中作为越冬策略，这似乎令人惊讶，但先前的研究表明，在这一地区有非常大密度的小型双壳类动物（Nucula belloti和Nuculana radiata，长1-3厘米）。每种双壳类对特定的沉积物粒度都有偏好，因此沉积模式和碳负荷的变化可能会极大地影响双壳类的种群结构。在过去的25年里，眼镜绒鸭的数量急剧下降，历史数据表明，在此期间，圣劳伦斯岛以南的优势双壳类群落也发生了变化。滑移区冰形成强度的可能变化，以及影响果阿冷池的相关运输条件的变化，可能影响了双壳类的种类和大小结构。模拟模型表明，这些猎物特征强烈地影响着绒鸭的能量收支。因此，绒鸭可能是气候介导的冰、水文、上层海洋生产和底栖生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获得资助的为期一年的海洋物理项目相互作用。物理海洋学计划将于1998年9月在圣劳伦斯岛南部部署一系列系泊处，以研究运输情况。与这一水文计划的合作将大大提高对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。这项合作还包括与利用SAR卫星图像实时调查海冰动态的科学家进行互动。合作的最终结果将是评估物理强迫功能（水文、冰）和营养过程（底栖动物到顶级捕食者）之间的相互作用。这将允许模拟羽绒的能量学和种群对不同冰情的敏感性，以及不同气候情景下底层底栖生物群落的变化。

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.