Impacts of infauna on sediment heterogeneity and acoustic propagation

Abstract

The sea floor is inhabited by diverse communities of animals that mix sediments through bioturbation and modify the physical properties of sediments. Infaunal activities, such as burrowing, construction of burrows and tubes, and ingestion and compaction of sediments into fecal pellets, can compact and dilate sediments and change grain size distribution on small scales. These impacts increase heterogeneity of sediment structure, potentially leading to increased acoustic attenuation, especially at higher frequencies, and increased variability in sound speed. We examined the impacts of infaunal communities from Mobile Bay, AL, and the New England Mud Patch on acoustic properties of sediments through measurements on sediment cores collected at each site. We measured sound speed and attenuation at six different orientations within a core and characterized the infaunal community within the core to determine how infauna affect variability in acoustic propagation. We hypothesize that infauna increase variability both on very small scales, among orientations within a core, and on local scales, among cores collected from the same site. These data are compared with acoustic measurements over a broader frequency range to determine how infauna affect variability in acoustic propagation both over different spatial scales and across a range of frequencies.