Relating functional diversity of infauna and sediment geoacoustic properties

Abstract

Marine sediments cover most of the seafloor and vary in physical structure from unconsolidated gravel or sand grains to cohesive, gel-like muds. Sediments also provide a habitat to diverse and abundant animals (infauna). Infauna are impacted by but can also affect the sediment’s physical and biogeochemical properties and fluid flow through and across the sediment. Through activities such as burrowing, feeding, and construction of tubes and rigid body parts, many infauna act as ecosystem engineers, directly and indirectly creating and changing their habitats. Characterization of infauna using functional groups based on how their activities affect their sediment environments can simplify the broad diversity of infauna. For example, some infauna create habitat structure in addition to modifying surface topography through tube construction. Others change sediment properties through bioturbation (animal-induced particle mixing) and bioirrigation (fluid mixing) as they burrow. Structure creation and bioturbation/irrigation can affect sediment geotechnical properties such as porosity, bulk density, grain size heterogeneity, fracture toughness, and stiffness. Changes in these properties can influence acoustic wave speed, attenuation, and backscatter. Thus, acoustics tools can be used to observe and quantify animal-sediment interactions relatively noninvasively by relating the activities of different functional groups with changes in acoustic properties of sediments.