Motor Mouth
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Kelly Dorgan is a University of Maine Ph.D. student in oceanography. She studies the mechanical behavior of marine sediments and how it affects sea worm burrowing. In her research, Dorgan found that marine worms burrow through muddy sediments by "cracking" rather than deforming them Photo by Eric Weissberger

Marine worm diggers are very familiar with the nasty bite sandworms can inflict. University of Maine researchers also know that the power of that mouth filled with tiny teeth is important for the species' mobility in mud.

Biomechanically, it was thought that worms burrow by pushing or excavating sediments. But UMaine marine researchers have demonstrated that the polychaete Nereis virens uses its mouth like a wedge to open cracks in muddy sediment. The sandworm burrows by turning its mouth inside out and applying pressure perpendicular to the direction of its motion, propagating the crack in the mud.

Muddy sediment acts like an elastic solid that fractures under force. By visualizing a worm's movement through seawater gelatin, which mimics the properties of mud, the researchers were able to characterize the stress field around a crack.

The process the sandworm employs could affect the movement of pollutants and other substances through mudflats. It also affects organic carbon fate (burial, resuspension or assimilation into animal biomass), which is important to the carbon cycle.

Among the researchers involved in the discovery are Ph.D. student Kelly Dorgan and Professor of Marine Sciences and Oceanography Peter Jumars, both at UMaine's Darling Marine Center; UMaine Professor of Civil Engineering Eric Landis; and Bruce Johnson and B.P. Boudreau of Dalhousie University, Halifax, Nova Scotia.

They reported their results in the February 2005 issue of the journal Nature. The story of their research also was featured in New Scientist magazine and the New York Times.