Collaborative Research: Effects of Flow on Feeding Behavior and Growth Rate of Interface-Feeding Benthos: Size-Dependent Changes and Recruitment Bottlenecks

以沉积或悬浮颗粒为食的成虫面临着从丰富的幼虫食物（浮游生物或蛋黄）到贫乏的成虫食物（与沉积物有关的有机物）的转变。体型小进一步限制了它们的消化和觅食能力，这可能会限制幼鱼专门寻找沉积物或底栖边界层中相对不稳定的食物（例如底栖硅藻、植物碎屑、富含有机物的絮凝体、动物猎物）。最近的研究揭示了几种界面摄食多毛动物的饮食变化的大小依赖性。虽然饮食变化的证据是明确的，但蠕虫在幼年到成年期间的进食活动是如何变化的还没有得到解决。对于在沉积物-水界面觅食的物种，已知它们会根据水动力条件在沉积物摄食和悬浮摄食之间切换，在幼年阶段更频繁的悬浮摄食可能是一种方法，通过这种方法，小蠕虫可能会提高它们的饮食质量和生长速度。这种依赖于摄食行为和生态位的变化可能对种群和群落动态产生重大影响。如果悬浮进食是幼鱼克服特定尺寸食物限制的主要手段，那么栖息地的水动力学特征将强烈影响幼鱼的生长速度和繁殖成虫阶段的招募速度。虽然水流对扩散和幼虫定居的影响已经受到了相当多的关注，但水流对幼鱼生长的影响是一个相对未被研究的生物-水流相互作用，它可能影响底栖生物种群和群落的结构和动态，就像水流对扩散和定居的影响一样显著。本研究的重点是四种蛛形多毛体，因为1)尽管蛛形多毛体是研究得最好的界面取食动物，但尺寸依赖性取食行为和生长速率尚未与流量相关；2)现有数据指出了几种蛛形纲的体型依赖性饮食变化和与食物相关的招募瓶颈；3)蛛形纲是许多底栖生物群落的丰富成员，在食物网和地球化学过程中起着核心作用。为了验证幼鱼比成年鱼更倾向于悬浮进食的假设，我们将在实验室水槽中观察不同流量和食物条件下个体的大小依赖进食行为。为了量化进食行为中尺寸依赖变化的营养后果，将在四个相同的、反向旋转的环形水槽中，在选定的流量和食物处理下，测量不同尺寸类别的生长率，这些水槽将被设置为流体动力学上不同的中生态系统。为了揭示与种内体型变化有关的取食机制和行为的物理约束，将在小体积水槽中量化颗粒捕获的速率和效率。为了更好地将实验室对个体的实验结果推断为密集的野外种群，将测试密度对幼鱼生长速度和颗粒摄取量的依赖效应。深入了解取食行为与力学、生长速率、颗粒特性和流速之间的联系，将为了解栖息地的水动力机制与蛛类种群的生长和成年期的招募速率之间的关系提供多方面和机制的理解。在教育和人力资源方面，合作努力结合并拓宽了博士后助理、初级教员和终身教员导师的专业知识。此外，整合行为观察和涉及生态、物理和生化参数的操作实验提供了一种理想的形式，可以向本科生介绍主要研究型大学和小型文理学院的跨学科研究。

Hentschel 0000951Juveniles of species that, as adults, feed on deposited or suspended particles face a transition from a rich larval diet (plankton or yolk) to a poor adult one (sediment-associated organics). Small body size further imposes digestive and foraging limitations that probably constrain juveniles to specialize on relatively labile foods in the sediment or benthic boundary layer (e.g. benthic diatoms, phytodetritus, organic-rich flocs, animal prey). Recent research has revealed size-dependent changes in the diets of several interface-feeding polychaetes. Although evidence of changing diets is clear, the ways in which worms' feeding activities shift as juveniles grow to adults is unresolved. For species foraging at the sediment-water interface and known to facultatively switch between deposit feeding and suspension feeding in response to hydrodynamic conditions, more frequent suspension feeding during the juvenile stage is a likely means by which small worms might increase the quality of their diet and their rate of growth. Such a size-dependent shift in feeding behavior and niche could have dramatic implications for population and community dynamics. If suspension feeding were the dominant means by which juveniles overcome size-specific food limitation, a habitat's hydrodynamic characteristics would strongly affect rates of juvenile growth and recruitment to the reproductive, adult stage. While flow's influence on dispersal and larval settlement has received considerable attention, flow-related effects on juvenile growth are a relatively unstudied organism-flow interaction that might impact the structure and dynamics of benthic populations and communities as significantly as flow's effects on dispersal and settlement.The study focuses on four species of spionid polychaetes because 1) although spionids are the best studied interface feeders, size-dependent feeding behavior and growth rates have not been measured in relation to flow; 2) existing data point to size-dependent diet changes and food-related recruitment bottlenecks in several spionids; and 3) spionids are abundant members of many benthic communities, playing central roles in food webs and geochemical processes. To test the hypothesis that juveniles tend to suspension feed more often than adults, the size-dependent feeding behavior of individuals will be observed in a laboratory flume under a variety of flow and food conditions. To quantify the nutritional consequences of size-dependent shifts in feeding behavior, growth rates of different size classes will be measured under selected flow and food treatments in four identical, counter-rotating annular flumes that will be set up as hydrodynamically distinct mesocosms. To reveal physical constraints on feeding mechanics and behavior in relation to intraspecific body-size variations, rates and efficiencies of particle capture will be quantified in a small-volume flume. To better extrapolate results from lab experiments on individuals to dense field populations, density--dependent effects on juvenile growth rate and particle ingestion will be tested. Insight into linkages among feeding behaviors and mechanics, growth rates, particle characteristics, and flow speed will provide a multifaceted and mechanistic understanding of the relationships between a habitat's hydrodynamic regime and the rates of growth and recruitment to adulthood in spionid populations.In terms of educational and human resources, the collaborative effort combines and broadens the expertise of a postdoctoral associate, a junior faculty member, and a tenured faculty mentor. In addition, integrating behavioral observations and manipulative experiments involving ecological, physical and biochemical parameters provides an ideal format to introduce undergraduates to interdisciplinary research at both a major research university and a small liberal-arts college.