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

底栖生物群落由丰富多样的生物组成，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量，将其转移到更高的营养水平，使营养物质再生，并决定沉积物中污染物和有机碳的命运。在许多沿海环境中，人为压力，包括富营养化及其导致的缺氧、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，评估物种多样性变化对生态和生物地球化学的影响几乎是不可能的。在沉积环境中，确定功能对与沉积物密切相关的生物尤其重要，例如在沉积物中生活和移动时摄取沉积物的动物沉积物捕食者。对单个物种的挖洞行为和形态进行了研究，但几十年来，即使是广泛的挖洞行为，也没有在不同的分类群中进行比较。此外，这种比较在很大程度上忽略了沉积物的力学响应，这种遗漏类似于研究游泳而不考虑流体力学。从那时起，在动物与沉积物相互作用的物理学方面取得了几项重大进展。泥质沉积物是有弹性的固体，通过裂缝可以延伸洞穴。相比之下，砂是颗粒状材料，其力学受作用于单个颗粒的重力的支配，而不是由粘聚合物基质的粘附和内聚支配泥浆力学。使用明胶作为泥浆的清晰模拟物，可以可视化挖掘和分析力和运动学。这项研究将结合明胶和沙子类似物中挖洞的结构和解剖学研究以及运动学分析，以及真实沉积物的力学测试和数值模拟。解剖结构、形态和行为之间的联系将与沙子和泥浆中的挖洞功能联系起来。多毛环节动物是底栖动物群落中丰富多样的组成部分，将是重点分类群。动物穴居的功能分类基于形态和营养作用，但沉积物力学的进展表明，类似的形态在砂和泥中可能具有不同的功能（例如，可膨胀结构在泥中延伸裂缝，但在砂中是锚）。此外，表面上不同的形态可能具有相似的功能（例如，Nereis virens的咽部和cirratliids Cirriformia moorei的肌肉前部都施加背腹压力以通过骨折扩展洞穴）。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角色和由此产生的底栖生物群落的功能多样性是重要的。本研究揭示的挖洞机制的多样性将使不同环境下的挖洞机制得到概括。掘洞运动的重要特征将被确定为不同掘洞者所共有的特征。在不同的环境中，我们将比较不同的砂和泥的物理约束对穴居动物形态和行为的影响。更广泛的影响。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，研究和教育将相结合。目标是使这些未来的科学家能够发展成功的跨学科沟通和合作所必需的技能。这里提出的可视化掘洞者的方法既经济又易于在课堂上使用。此外，在生物学研究中纳入相关的物理学，特别是连续介质力学，是很重要的，但在适当的课程中往往被忽视。课程将通过ASLO和SICB教育网站开发和共享。由于果冻中的蠕虫已经引起了公众的兴趣，这些结果的广泛传播应该加强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，将制作一个关于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1.4万名订阅者，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.