Bioturbation.

Bioturbation is an umbrella term for the biological reworking of soils and sediments by all kinds of organisms. It includes not only the impact of animals, but also that of rooting plants and trees. Although Charles Darwin's last scientific book On the Formation of Vegetable Mounds through the Action of Worms with Observations on their Habits (1881) already reported pioneering observations on the role of earthworms in particle displacement, soil formation and erosion-sedimentation processes, the term bioturbation was only introduced 70 years later to describe fossil biogenic structures in sedimentary rocks. We now know that bioturbation plays a major role in soil formation, geomorphology, sediment stability, structure and texture, and impacts the distribution, diversity and functioning of microbes and global biogeochemical cycles. As such, bioturbation is studied by biologists, ecologists, soil scientists, sedimentologists, biogeochemists, civil and environmental engineers, paleontologists and paleoceanographers. Here we focus on bioturbation by animals in the Earth's largest ecosystem, the seafloor, but bioturbation is also a key factor in freshwater sediments, wetlands and terrestrial soils.