Mw. Denny et Ca. Blanchette, Hydrodynamics, shell shape, behavior and survivorship in the owl limpet Lottia gigantea, J EXP BIOL, 203(17), 2000, pp. 2623-2639
On wave-swept rocky shores, limpets are subjected to water velocities in ex
cess of 20 ms(-1), which may impose large hydrodynamic forces, Despite the
extreme severity of this flow environment, predictions from conical models
suggest that limpets' shells are typically far from the optimal shape that
would minimize the risk of dislodgment, a deviation that is allowed by the
high tenacity of the limpets' adhesive system, In this study, we test this
conclusion using an actual limpet. The shell of Lottia gigantea differs sub
stantially from the hydrodynamic optimum in that its apex is displaced ante
riorly to form a plough, which is used to defend the limpet's territory, Th
e hydrodynamic effects of this shape are similar to those observed in conic
al models: the animal experiences an increased lift when facing into the ho
w and a decreased lift when the how is at its back. However, neither effect
has a substantial impact on the risk of dislodgment, When the animal is st
ationary, its adhesion to the substratum is very strong, and its risk of be
ing dislodged is small regardless of its orientation to the how and despite
its sub-optimal shape. In contrast, when the animal is crawling rapidly, i
ts adhesion is substantially decreased, and it would probably be dislodged
by rapid flow even if the shell were shaped optimally, The risk of dislodgm
ent by waves is therefore functionally independent of shell shape. In essen
ce, despite the extremely high water velocities to which this species is su
bjected, its shell has had the 'permission' of the flow environment to resp
ond to other selective factors, in particular those associated with its agg
ressive, territorial behavior, The result is a shell that is both a potent
territorial weapon and a functional (albeit less than optimal) hydrodynamic
shape.