The tenacity of the limpet, Patella vulgata L.: An experimental approach

It has been shown that adhesion of the limpet, Patella vulgata L. is influenced by both physical and physiological factors. The tenacity is sensitive to surface properties of the substratum, varying inversely with the contact angle which water makes with a substratum. This can be explained in terms of thermodynamics. Surface roughness also affects tenacity and this is explained in the same manner. Different angles of detachment were tested and it was clearly shown that when a strong peeling component was introduced, a much reduced force was needed to detach a limpet. Contrary to a normal pull, when a shear pull is exerted the force is not proportional to the surface area of the foot. It has also been shown that the speed of separation affects the measured tenacity; there is a speed at which tenacity will be maximum. The effect of water temperature on tenacity has been tested, tenacity increasing with rising temperature (7, 13, 20 °C). At the higher temperatures limpets are able to contract the foot muscles more powerfully, indicating that increased foot rigidity increases tenacity. By measuring the tenacity of limpets left out of water for different periods of time it has been shown that desiccation has no effect on tenacity, but a change from aquatic to aerial respiration increases tenacity. Tenacity has also been measured when the limpets have been subjected to a reduction in metabolic rate. The effect of both anoxia and narcotization shows that reduced muscle tonus, especially in the foot, results in decreased tenacity. These results further demonstrate that foot rigidity is essential for efficient adhesion. Eimpets from different habitats (exposed and sheltered) and vertical distribution (high and low level on shore) exhibited no differences in tenacity. During locomotion limpets leave a mucous trail, most of the mucus being confined to the edge of the trail. Water is incorporated anteriorly under each new locomotory wave and these pockets of water are used to release the mucus from the substratum during locomotion. It is concluded from this study that limpet adhesion can be explained solely by the tackiness of the pedal mucus, tack being due to the stored elastic energy within the mucous layer itself.