CAREER: Mechanisms of bioturbation and ecosystem engineering by benthic infauna

海洋沉积物是丰富多样的生物群落的重要栖息地，这些生物群落是较高营养水平的重要食物来源，包括商业上重要的物种。通过挖洞、建造管道和以沉积物为食，这些动物改变了它们的物理和化学环境，以至于它们被认为是生态系统工程师。生物扰动，即动物对沉积物的混合，对于营养物质的再生以及污染物和结合在矿物颗粒上的碳的运输非常重要。尽管它很重要，但我们从群落结构预测生物扰动率和模式的能力很差，这主要是因为我们缺乏对动物混合沉积物的机制的了解。该项目建立在早期工作的基础上，表明动物通过破裂在泥质沉积物中延伸洞穴，以检验沉积物的力学性质影响挖掘机制也影响沉积物混合的假设。更广泛地说，这个项目考察了(I)生物体在群落中的功能作用，(Ii)沉积物的机械性质，以及(Iii)可能增加或减少动物活动的因素，如温度和食物供应对生物扰动率的相对贡献。穴居动物改变了沉积物的物理性质，该项目量化了这些变化，并测试了这些变化具有重要生态意义并影响干扰后群落演替的假设。除了这一更广泛的科学影响外，该项目还包括开发测量沉积物性质的仪器，并包括一项实质性的教育计划，向研究生、本科生和中学生介绍技术在海洋科学中发挥的重要作用。通过挖洞和觅食活动，底栖动物混合沉积物并改变其物理环境。生物扰动阻碍了有机质的埋藏，促进了营养物质的再生，并抹黑了古生物和地层记录。然而，目前对底栖生物活动混合沉积物的机制的了解不足以预测生物扰动驱动的底栖生物群落结构变化对重要沉积物生态系统功能的影响。该项目测试与动物群、生物扰动和岩土特性相关的特定假设，最终目的是了解动物群与其物理环境之间的动态变化和潜在的反馈。该项目综合了野外和实验室实验，以评估底栖动物群落结构和活动对生物扰动率的相对重要性。此外，该项目建立在最近的工作基础上，表明泥质沉积物是一种弹性凝胶，蠕虫通过弹性凝胶通过断裂来扩展洞穴，从而提出沉积物的岩土性质通过控制在洞穴扩展过程中从沉积物基质中释放的颗粒来调节生物扰动。有限元模拟确定了钻探过程中裂隙释放的颗粒如何取决于沉积物的断裂韧性(粘聚力)和硬度(压实)，并补充了表征岩土特性对钻探行为影响的实验室实验。这项拟议的研究还旨在确定非动物群对岩土特性的影响是否具有生态重要性。在一次实验物理干扰后，海底群落和岩土属性的变化解决了这样的假设，即对大宗沉积物属性的生态系统工程有助于成功。该奖项反映了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。

Marine sediments are important habitats for abundant and diverse communities of organisms that are important as food sources for higher trophic levels, including commercially important species. Through burrowing, constructing tubes, and feeding on sediments, these animals modify their physical and chemical environments to such an extent that they are considered ecosystem engineers. Bioturbation, the mixing of sediments by animals, is important in regenerating nutrients and transporting pollutants and carbon bound to mineral grains. Despite its importance, our ability to predict bioturbation rates and patterns from the community structure is poor, largely due to a lack of understanding of the mechanisms by which animals mix sediments. This project builds on earlier work showing that animals extend burrows through muddy sediments by fracture to test the hypothesis that the mechanical properties of sediments that affect burrowing mechanics also affect sediment mixing. More broadly, this project examines the relative contributions of (i) the functional roles of the organisms in the community, (ii) the mechanical properties of sediments, and (iii) factors that might increase or decrease animal activity such as temperature and food availability to bioturbation rates. Burrowing animals modify the physical properties of sediments, and this project quantifies these changes and tests the hypothesis that these changes are ecologically important and affect community succession following a disturbance. In addition to this scientific broader impact, this project involves development of instrumentation to measure sediment properties and includes a substantial education plan to introduce graduate, undergraduate, and middle school students to the important role that technology plays in marine science. Through burrowing and feeding activities, benthic infauna mix sediments and modify their physical environments. Bioturbation gates the burial of organic matter, enhances nutrient regeneration, and smears the paleontological and stratigraphic record. However, current understanding of the mechanisms by which infaunal activities mix sediments is insufficient to predict the impacts of changes in infaunal community structure on important sediment ecosystem functions driven by bioturbation. This project tests specific hypotheses relating infaunal communities, bioturbation, and geotechnical properties with the ultimate goal of understanding the dynamic changes and potential feedbacks between infauna and their physical environments. This project integrates field and lab experiments to assess the relative importance of infaunal community structure and activities to bioturbation rates. Additionally, this project builds on recent work showing that muddy sediments are elastic gels through which worms extend burrows by fracture to propose that geotechnical properties of sediments mediate bioturbation by governing the release of particles from the sediment matrix during burrow extension. Finite element modeling determines how the release of particles by fracture during burrowing depends on the fracture toughness (cohesion) and stiffness (compaction) of sediments and complements laboratory experiments characterizing the impact of geotechnical properties on burrowing behaviors. The proposed research also aims to determine whether impacts of infauna on geotechnical properties are ecologically important. Changes in infaunal communities and geotechnical properties following an experimental physical disturbance address the hypothesis that ecosystem engineering of bulk sediment properties facilitates succession.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.