Functional diversity of infaunal burrowers: Towards a mechanistic understanding of animal-sediment interactions

底栖生物群落由多种多样的生物组成，具有重要的生态和生物地球化学作用。 它们将有机碳转化为生物质，生物质被转移到更高的营养水平，再生营养物质，并决定污染物和埋藏在沉积物中的有机碳的命运。 在许多沿海环境中，人为压力，包括富营养化和由此造成的缺氧、拖网捕捞和渔业干扰以及污染物，对物种多样性产生了负面的、往往是巨大的影响。 然而，如果不了解物种的功能作用，就几乎不可能评估物种多样性变化对生态和生物地球化学的影响。 在沉积环境中，确定功能对于与沉积物密切相关的生物尤其重要，例如生活在沉积物中并在沉积物中移动时摄取沉积物的底栖存款饲养者。穴居行为和形态已被检查的个别物种，但几十年过去了，因为即使是广泛的穴居行为进行了比较，在不同的类群。 此外，这种比较在很大程度上忽略了沉积物的机械反应，这类似于研究游泳而不考虑流体力学。 自那时以来，在动物-沉积物相互作用的物理学方面取得了若干重大进展。 泥质沉积物是弹性固体，洞穴通过断裂延伸。 相比之下，砂是粒状材料，其力学由作用于单个颗粒的重力控制，而不是由粘聚合物基质的粘附力和凝聚力控制泥浆力学。 使用明胶作为泥浆的清晰模拟物，可以实现钻孔的可视化以及力和运动学的分析。 这项研究将结合联合收割机的结构和解剖学研究和运动学分析，在明胶和砂模拟与力学测试和数值模拟的真实的沉积物。 在解剖学、形态学和行为学之间建立联系，以在砂和泥中挖掘功能。 底栖生物群落中种类丰富的多毛类环节动物将成为重点分类单元。穴居动物的功能分组一直基于形态和营养作用，但沉积力学的进展表明，类似的形态在砂和泥中可能具有不同的功能（例如，可膨胀结构在泥浆中延伸裂缝，但在砂中是锚定件）。 此外，看似不同的形态可能具有类似的功能（例如，沙蚕的咽部和硬脊线虫的肌肉前部都通过断裂产生背腹应力来扩展洞穴）。 将功能与穴居动物的形态和行为联系起来，对于理解底栖动物的功能作用和由此产生的底栖生物群落的功能多样性具有重要意义。 本研究所揭示的挖洞机制的多样性将使不同环境下的挖洞机制具有普遍性。 穴居运动的重要特征将被确定为不同的穴居动物所共有的。 沙和泥的不同物理约束如何指定穴居力学和影响穴居动物的形态和行为，将针对来自不同环境的密切相关类群进行对比。 研究和教育将通过招募来自不同领域的本科生并让他们参与与这项跨学科研究相关的团队研究项目来整合。 我们的目标是使这些未来的科学家能够发展跨学科成功沟通和合作所需的技能。 这里提出的可视化穴居人的方法是经济的，易于纳入类。 此外，将相关的物理学，特别是连续介质力学，在生物学研究是重要的，但往往被忽视，在适当的课程。 将通过ASLO和SICB教育网站制定和分享课程。 由于果冻中的蠕虫已经引起了公众的兴趣，因此这些结果的广泛传播应该会提高对蠕虫在沉积物中挖洞的机制和相关主题的科学理解。 与SIO的公共信息办公室Scripps Communications合作，将制作有关这项研究的视频播客。 该播客将在斯克里普斯海洋学研究所的“探索”电子杂志（explorations.ucsd.edu）上播出，该杂志拥有14,000名订阅者，并将通过SciVee与其他观众进行比较。

Benthic communities comprise diverse and abundant organisms with important ecological and biogeochemical roles. They convert organic carbon into biomass that is transferred to higher trophic levels, regenerate nutrients, and determine the fate of pollutants and organic carbon buried in sediments. In many coastal environments, anthropogenic stresses, including eutrophication and resulting hypoxia, trawling and disturbance from fisheries, and pollutants have negative and often dramatic affects on species diversity. Assessing the ecological and biogeochemical impacts of changes in species diversity is nearly impossible, however, without understanding the functional roles of the species. In sedimentary environments, determining functionality is especially important for organisms closely associated sediments, such as infaunal deposit feeders that ingest sediments while living in and moving through them. Burrowing behaviors and morphologies have been examined for individual species, but decades have passed since even broad burrowing behaviors were compared across diverse taxa. Moreover, such comparisons largely ignored the mechanical response of sediments, an omission similar to studying swimming without considering fluid mechanics. Since that time, there have been several major advances in the physics of animal-sediment interactions. Muddy sediments are elastic solids through which burrows are extended by fracture. In contrast, sands are granular materials whose mechanics are governed by gravitational forces acting on individual grains, rather than by adhesion and cohesion of the mucopolymeric matrix dominating mud mechanics. Use of gelatin as a clear analog for muds has enabled visualization of burrowing and analyses of forces and kinematics. This research will combine structural and anatomical studies and kinematic analyses of burrowing in gelatin and sand analogs with mechanical testing and numerical modeling of real sediments. Linkages would be made among anatomies, morphologies, and behaviors to burrowing function in sands versus muds. Polychaetous annelids, a diverse and abundant component of benthic communities, will be the focal taxon. Functional groupings of burrowing infauna have been based on morphologies and trophic roles but advances in sediment mechanics suggest that similar morphologies may have different functions in sands versus muds (e.g., expansible structures extend cracks in muds but are anchors in sands). In addition, seemingly different morphologies may have analogous functions (e.g., the pharynx of Nereis virens and the muscular anterior of the cirratulid Cirriformia moorei both exert dorso-ventral stress to extend burrows by fracture). Linking functions to morphologies and behaviors of burrowers is important in understanding functional roles of infauna and resulting functional diversity of benthic communities. The diversity of burrowing mechanisms revealed in this study will enable generalizations about burrowing mechanics in different environments. Important characteristics of burrowing locomotion will be identified as those shared by diverse burrowers. How the different physical constraints of sand and mud specify burrowing mechanics and affect morphologies and behaviors of burrowers will be contrasted for closely related taxa from different environments.Broader Impacts. Research and education will be integrated by recruiting undergraduates from different fields and involving them in team research projects associated with this interdisciplinary study. The goal is to enable these future scientists to develop skills necessary for successful communication and collaboration across disciplines. The methods of visualizing burrowers proposed here are economical and easy to incorporate in classes. Moreover, incorporating relevant physics, especially continuum mechanics, in biology studies is important, yet often neglected, in suitable courses. Curricula will be developed and shared through ASLO and SICB educational websites. Because worms in Jell-O have already captured the interest of the general public, broad dissemination of these results should enhance scientific understanding of the mechanics of worm burrowing in sediments, and related topics. In collaboration with Scripps Communications, the public information office of SIO, a video podcast about this research will be produced. The podcast will be featured in Scripps Institution of Oceanography's "Explorations" electronic magazine (explorations.ucsd.edu), which has 14,000 subscribers and would reach comparisons of additional viewers through SciVee.