BOLLER, M.L.*; CARRINGTON, E.; Univeristy of Rhode Island: Drag and flexibility in Chondrus crispus Stackhouse: what drives the Vogel Number?

The reorientation of an intertidal alga with the flow of a crashing wave allows the alga to reduce drag by reducing the area projected into flow. This phenomenon, dubbed reconfiguration, manifests itself as a change in the exponent used to scale water velocity to drag (the Vogel number). While it is intuitive that objects that are less stiff easily reconfigure in flow, little work has been done to quantify how variability in tissue stiffness will influence the drag of an organism in flow. Chondrus crispus was used as a model organism to study the effects of stiffness on drag. Because a C. crispus thallus represents a very complex beam, the degree to which an individual will reconfigure will depend on the Young�s modulus of the tissue, thallus cross-sectional area, shape, and length, and application of the force. Drag and reconfiguration were measured on individual thalli at a range of water velocities. Speed specific drag was plotted against water velocity to determine the Vogel number. Morphology was characterized for each thallus and material properties of several branch orders were determined with a tensometer. Preliminary data suggest that the reconfiguration in the crown of the thallus drives the Vogel number rather than the initial large reconfiguration of the stipe seen at low velocities. The relationships among thallus morphology, material properties, and Vogel number will be discussed.