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Biomechanics of flexible body plans


Divers deploying instrumentation in subtidal habitats offshore. Photo courtesy of C. Nelson.
Unlike human-fabricated objects or structures which are built using relatively stiff materials like metals, hard plastics, concrete, and wood, organisms in nature often rely on flexible, stretchy (and even soft and squishy) materials.  Historically, studies of mechanically compliant materials in organisms have emphasized their potential benefits, noting for example the success of weak and flimsy seaweeds even in wave-battered locations, and suggesting that extensibility provides a viable alternative to the more traditional "strong and rigid" structural paradigm that humans have embraced. Our lab group and colleagues, however, have shown that these advantages are only part of the story.  Organisms that move in response to applied forces develop momentum, and this property can strongly affect the dynamics of motion and how far a plant or animal is bent or pulled.  Such consequences have important implications for understanding the disturbance ecology of critical habitat-forming subtidal and intertidal seaweeds, among many other species. 

Sea anemones growing on the kelp, Pterygophora californica, a seaweed with a flexible stem-like stipe

Our approach in examining the implications of compliant body plans has involved both  mathematical modeling and field and laboratory experiments, and has taken us into arenas often viewed as the terrain of engineers and physicists.  A big difference, of course, is that our interests are fundamentally biological.  We strive to understand the connection of organisms to their natural environments, how they cope with the physical stresses they encounter, and the resultant consequences of such interactions for ecological performance.

Selected publications:

Gaylord, B., and M.W. Denny.  1997.  Flow and flexibility I: Effects of size, shape, and stiffness in determining wave forces on the stipitate kelps, Pterygophora californica and Eisenia arborea.  Journal of Experimental Biology 200: 3141-3164.

Denny, M.W., B.P. Gaylord, and E.A. Cowan.  1997.  Flow and flexibility II: The roles of size and shape in determining wave forces on the bull kelp, Nereocystis luetkeana.  Journal of Experimental Biology 200: 3165-3183.

Denny, M., B. Gaylord, B. Helmuth, and T. Daniel.  1998.  The menace of momentum: Dynamic forces on flexible organisms.  Limnology and Oceanography 43: 955-968.

Gaylord, B., B.B. Hale, and M.W. Denny.  2001.  Consequences of transient fluid forces for compliant benthic organisms.  Journal of Experimental Biology 204: 1347-1360.

Denny, M., and B. Gaylord.  2002.  The mechanics of wave-swept algae.  Journal of Experimental Biology 205: 1355-1362.

Gaylord, B., M.W. Denny, and M.A.R. Koehl.  2003.  Modulation of wave forces on kelp canopies by alongshore currents.  Limnology and Oceanography 48: 860-871.

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