Meeting Abstract
Seaweeds survive on wave-swept shores primarily by being flexible, which poses a problem for coralline algae because their calcified cell walls are rigid. Approximately 100 million years ago, crustose coralline algae evolved a key adaption – joints – that renders them flexible and has allowed the resulting articulated corallines to dominate space on some of Earth’s most wave-beaten coasts. The material from which these joints are constructed has unusual mechanical properties: it is eight times as extensible and four times are strong as typical algal tissue, and is immune to the fatigue that normally accompanies repeated impositions of force. In this talk, we report on new measurements of joint material properties: creep, the strain-rate dependence of stiffness, and the behavior of the material when subjected to cyclic loading. These measurements, when combined with previous information, allow us to formulate a simple model that explains how the chemical composition and macromolecular structure of cell-wall material accounts for the material’s unusual properties. We propose that cell wall material is a fiber-reinforced composite in which cellulose provides the fibers and a galactan gel forms the matrix. The fibers are not crosslinked, which allows the material to creep indefinitely, but the viscosity of the matrix ensures that the material is both elastic and strong when subjected to wave-induced fluid-dynamics forces. Our model makes predictions (e.g., the wrapping angle of cellulose fibers) that can be tested by future measurements.
