The diversity of form among benthic marine plants and animals on rocky coasts is remarkable. Stiff and strong organisms grow alongside others that are compliant and flimsy. Given the severity of wave action on many shores and thus the potential for the imposition of large hydrodynamic forces, this immediately raises the question of how, from this overall spectrum of designs, flexible and weak organisms survive. A number of explanations have been proposed, most emphasizing one or more of several possible advantages of deformability. Here, we explore quantitatively two of the more common of these explanations: (i) that strength can be traded against extensibility in allowing stretchy organisms to withstand transient wave forces, and (ii) that greater compliance (and thus longer organism response times) allows universally for the amelioration of brief loads. We find that, although these explanations contain kernels of validity and are accurate for a subset of conditions, they are not as general as has often been assumed.

Bell
E. C.
,
Gosline
J. M.
(
1996
).
Mechanical design of mussel byssus: material yield enhances attachment strength.
J. Exp. Biol
199
,
1005
–.
Gaylord
B.
,
Denny
M. W.
(
1997
).
Flow and flexibility. I. Effects of size, shape and stiffness in determining wave forces on Vx = A. 2 t 2(A6) V =. Mx (A5)=. 2 x 2(A4) M = EIE visc I, t (A3)1360the stipitate kelps Eisenia arborea and Pterygophora californica.
J. Exp. Biol
200
,
3141
–.
Harvell
C. D.
,
LaBarbera
M.
(
1985
).
Flexibility: a mechanism for control of local velocities in hydroid colonies.
Biol. Bull
168
,
312
–.
Johnson
A. S.
(
1993
).
Sag-mediated modulated tension in terebellid tentacles exposed to flow.
Biol. Bull
185
,
10
–.
Johnson
A. S.
,
Koehl
M. A. R.
(
1994
).
Maintenance of dynamic strain similarity and environmental stress factor in different flow habitats: thallus allometry and material properties of a giant kelp.
J. Exp. Biol
195
,
381
–.
Koehl
M. A. R.
(
1977
).
Effects of sea anemones on the flow forces they encounter.
J. Exp. Biol
69
,
87
–.
Koehl
M. A. R.
(
1982
).
The interaction of moving water and sessile organisms.
Scient. Am
247
,
124
–.
Koehl
M. A. R.
(
1984
).
How do benthic organisms withstand moving water?.
Am. Zool
24
,
57
–.
Lillie
M. A.
,
Gosline
J. M.
(
1996
).
Swelling and viscoelastic properties of osmotically stressed elastin.
Biopolymers
39
,
641
–.
Patterson
M. R.
(
1984
).
Patterns of whole colony prey capture in the octocoral, Alcyonium siderium.
Biol. Bull
167
,
613
–.
Purslow
P.
(
1991
).
Notch-sensitivity of non-linear materials.
J. Materials Sci
26
,
4468
–.
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