Meeting Abstract
Soft sediment dwellers gain protection and nutrition from the particulate world in which they live but are limited by their abilities to move within and upon this dense, gritty, shifting medium. False Bay, WA offers sedimentary landscapes from well-sorted sands to muds. By studying species that vary in body softness, stretchiness, and locomotor ability in addition to the material properties of the sediment in which they live, we achieve an organismal view of the physical challenges of this habitat. Sediment stiffness separates the distribution of two closely related polychaete species, Abarenicola pacifica and Abarenicola claparedi, within False Bay. Transplant experiments show that A. claparedi is a weak burrower and cannot successfully enter the stiffer habitat of A. pacifica. A. pacifica can burrow in all tested sediments, but may not be able to maintain a burrow in the more collapsible, less stiff regions of False Bay. The viscoelastic body of the burrowing sea cucumber Leptosynapta clarki allows it to slowly, inexorably extend its body through the dense medium as its tentacles make space by shifting sand grains. This is in contrast to the relatively rapid burial of Metacarcinus magister and Cancer productus that can bury in all regions of False Bay (although efficacy varies with species and sediment stiffness). Crabs use their posterior legs to disrupt the sediment and then anchor their bodies as their claws push this unconsolidated sediment away. To remain on the surface of the sediment, the bubble snail, Haminoea vesicula, must resist drag. By partial burial, it can quickly cover its body with a sheet of sediment-encrusted mucus increasing its effective density and lowering its profile. The morphologies and techniques of these different taxa provide organismal perspectives on a variety of physical challenges of sedimentary habitats even within this single bay.
