The role of biological processes in muddy sediments

Abstract

Muddy sediments are inhabited by diverse communities of animals that burrow, construct and irrigate tubes, ingest and egest sediments, and produce hard structures such as shells and exoskeletons. These infaunal animals mix sediments through bioturbation and modify the physical properties of sediments. Bulk density can be increased through compaction along burrow walls and production of compact fecal pellets or decreased by excavation of burrows and mixing of compacted sediments. Burrows and other biogenic structures can increase heterogeneity and consequently sound attenuation. Characterization of infauna using functional groups based on how their activities and body types affect their sediment environments can simplify the diversity of these animals. Some species, such as those that build tubes from shell fragments, have a disproportionately large impact on acoustics. Both infaunal and microbial communities feed on and modify the organic matter in muds, which may affect grain-grain interactions. Understanding the effects of biological processes on acoustics is important in interpreting acoustic data both in the upper layer of sediments and in deeper layers in which paleo-biological activities are preserved as well as in using acoustics as a tool for studying infaunal communities and their activities.