Meeting Abstract
Muddy sediments are elastic solids through which morphologically diverse animals extend burrows by fracture. Muddy sediments inhabited by burrowing infauna vary considerably in mechanical properties, however, and at high enough porosities, muds can be fluidized. In this study, we examined burrowing behaviors and mechanisms of burrow extension for three morphologically diverse polychaetes inhabiting soft muddy sediments. Worms burrowed in gelatin, a transparent analog for muddy sediments, and in natural sediments in a novel viewing box enabling visualization of behaviors and sediment responses. Scalibregma inflatum and Sternaspis scutata can extend burrows by fracture but both also extended burrows by plastic deformation or rearrangement of sediment aggregates and by combinations of fracture and plastic deformation. Mechanical responses of sediments corresponded with different burrowing behaviors of Scalibregma, which uses direct peristalsis to extend burrows by fracture or a combination of plastic deformation and fracture and uses a retrograde expansive peristaltic wave to extend burrows by plastic deformation. Burrowing speeds differed between behaviors and sediment mechanical responses, with slower burrowing associated with plastic deformation. Sternaspis exhibited less variability in behavior and burrowing speed but did extend burrows by different mechanisms consistent with observations of Scalibregma. Ophelina acuminata did not extend burrows by fracture, rather plastically deformed sediments similarly to the related Armandia brevis. Our results extend the range of natural sediments in which burrowing by fracture occurs but the dependence of burrow extension mechanism on species, burrowing behavior, and burrowing speed highlights the need for better understanding of mechanical responses of sediments to burrowers.
