Meeting Abstract
P1.89 Friday, Jan. 4 Are they stuck in the mud: Sediment properties and the burrowing abilities of two species of lugworm in False Bay, Washington CRANE, R.L.*; MERZ, R.A.; Swarthmore College; Swarthmore College rcrane140@gmail.com
If burrowing organisms use crack propagation to move through the sediment, then the material properties of the sediment affecting crack growth should relate to animal distribution and their success in burrowing. Material properties of the sediment are also likely to be related to grain size distribution. To test these ideas we examined two morphologically similar species of lugworm that inhabit different areas of False Bay, WA. We developed a penetration test to quantify the stiffness of undisturbed sediment in the field at sites inhabited by either Abarenicola pacifica or Abarenicola claparedi. We collected sediment cores at these sites and analyzed their grain size distributions. A. pacifica lived exclusively in stiffer, poorly-sorted sediments with a high proportion of silts and clays, while A. claparedi were found only in less stiff, well-sorted sediments dominated by fine sands (0.125-0.250 mm). Additionally, we observed and timed individuals of both species burrowing in the field in both types of undisturbed sediment. A. claparedi struggled in the stiff sediment. They were slower to initiate successful burrows and when they did so burrowed at shallower angles. In contrast, in both sediment types, A. pacifica initiated burrows more quickly and typically constructed nearly vertical burrow shafts. Although larval settlement initially dictates the distribution of these species, both are reported to periodically relocate as juveniles or adults. Our experiments show that if this is true, A. claparedi would be unsuccessful in moving into or through stiffer muddy sediments. A. pacifica would not seem to be limited by initiating a burrow in softer sediments associated with A. claparedi, but its exclusion from these areas suggests that it is limited by some other factor.
