Skip to main content
padlock icon - secure page this page is secure

Free Content Worms as wedges: Effects of sediment mechanics on burrowing behavior

Download Article:
(PDF 465 kb)
Recent studies document linear elastic response of muddy marine sediments to load and deformation on temporal and spatial scales relevant to animal movement, with burrowers making openings for movement in such sediments by fracture. Cracks propagate through linear elastic solids in mode I (opening-mode crack growth) when the stress intensity factor (KI) at the crack tip exceeds the material's fracture toughness (KIc). Fracture mechanics depend on material stiffness as well as fracture toughness, and we prepared a range of transparent gels that varied in stiffness and fracture toughness to assess the dependence of burrowing behavior on these material properties. When the polychaete Nereis virens elongated its burrow, it altered its body shape and behavior across these gels in a manner consistent with fracture mechanics theory. We modeled burrow elongation as stable, wedge-driven crack growth, and calculated that KI values at the tips of the burrows reached KIc values of most gels without pharynx eversion and exceeded KIc when the pharynx was everted. In materials with higher fracture toughnesses, worms everted their pharynges to become thicker and blunter wedges, as predicted from simple wedge theory. In stiff materials with low toughness, worms moved their heads from side-to-side to extend crack edges laterally, relieving elastic forces compressing them and allowing them to maintain body shape more easily. This solution extends the crack in small increments that each require relatively little force. We introduce a dimensionless “wedge” number to characterize the relative importance of work to fracture the material and extend the burrow and work to maintain body shape against the elastic restoring force of the material. The mechanism of burrowing by crack propagation is utilized across a range of material properties found in natural muds, and variation in these properties strongly influences burrowing behaviors. These results demonstrate how quantifying the mechanical properties of muds can improve our understanding of bioturbation. On spatial and temporal scales relevant to burrower activity, variations in these properties may impact particle mixing by influencing burrower behavior.

15 References.

No Supplementary Data.
No Article Media
No Metrics

Document Type: Research Article

Publication date: March 1, 2008

More about this publication?
  • The Journal of Marine Research, one of the oldest journals in American marine science, publishes peer-reviewed research articles covering a broad array of topics in physical, biological and chemical oceanography. Articles that deal with processes, as well as those that report significant observations, are welcome. Biological studies involving coupling between ecological and physical processes are preferred over those that report systematics. The editors strive always to serve authors and readers in the academic oceanographic community by publishing papers vital to the marine research in the long and rich tradition of the Sears Foundation for Marine Research. We welcome you to the Journal of Marine Research.
  • Editorial Board
  • Information for Authors
  • Subscribe to this Title
  • Ingenta Connect is not responsible for the content or availability of external websites
  • Access Key
  • Free content
  • Partial Free content
  • New content
  • Open access content
  • Partial Open access content
  • Subscribed content
  • Partial Subscribed content
  • Free trial content
Cookie Policy
Cookie Policy
Ingenta Connect website makes use of cookies so as to keep track of data that you have filled in. I am Happy with this Find out more