Meeting Abstract

97.3  Sunday, Jan. 6  Meandering through marine muds: kinematics of burrowing and swimming by the polychaete Armandia brevis DORGAN, K.M.*; LAW, C.J.; ROUSE, G.W.; Scripps Institution of Oceanography; Scripps Institution of Oceanography; Scripps Institution of Oceanography kdorgan@ucsd.edu

Mechanical interactions between organisms and their environments are integral to locomotion, but mechanical responses of soils and sediments to forces applied by burrowing organisms are poorly understood. Recent work has shown that muddy sediments are elastic solids through which animals extend burrows by fracture. However, Armandia brevis, a mud-burrowing opheliid polychaete annelid, lacks an expansible anterior consistent with fracturing mud, and instead uses undulatory movements to burrow. Here we show that A. brevis neither fractures nor fluidizes sediments, but instead uses a third mechanism, plastically rearranging sediment grains to create a burrow. In addition, the curvature of the undulating body fits meander geometry used to describe rivers, and changes in curvature over time driven by muscle contraction are similar for swimming and burrowing worms, indicating that the same gait is used in both media. Large calculated friction forces for undulatory burrowers suggest that sediment mechanics affect undulatory and peristaltic burrowers differently; undulatory burrowing may be more effective for small worms that live in sediments not compacted or cohesive enough to extend burrows by fracture.