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Shell clamping behaviour in the limpet Cellana tramoserica

Gary K. Ellem^1,*, John E. Furst² and Kenneth D. Zimmerman²

¹ Department of Biological Sciences, University of Newcastle, Callaghan, NSW 2308, Australia and
² School of Science and Technology, Central Coast Campus, University of Newcastle, Brush Road, Ourimbah, NSW 2258, Australia

View larger version (11K): [in a new window]   Fig. 1. A force diagram describing the forces acting during wave action. The model assumes that the limpet clamps its shell against the substratum in order to generate friction to resist horizontal shear.

View larger version (23K): [in a new window]   Fig. 2. Clamping measurement apparatus. The upper load cell was used to measure the simulated lift force applied to the limpet by the piston; the lower load cell measured the force of pedal adhesion.

View larger version (13K): [in a new window]   Fig. 3. Performance curve for the force application apparatus. The mechanical output matched that predicted by the electronic input for force application rates up to 1000 N s–1. The line is theoretical. , Cellana tramoserica; , suction cap.

View larger version (1K): [in a new window]   Fig. 4. A typical experiment for the limpet Cellana tramoserica exposed to a simulated wave force. The adherence force (FAdherence) of the foot was consistently greater than the lift force (FLift). The force difference between the adherence and lift force was generated by the action of shell clamping by the limpet (FClamping) (hatched area).

View larger version (17K): [in a new window]   Fig. 5. Force/time curve in the absence of the limpet Cellana tramoserica. The transient force difference seen at the onset of the lift force (circled) was a result of elasticity in the double-sided tape connecting the two force sensors.

View larger version (12K): [in a new window]   Fig. 6. The force of shell clamping as a function of the lift force for the limpet undergoing the simulated wave profile shown in Fig. 4.

View larger version (12K): [in a new window]   Fig. 7. The degree of shell clamping in response to applied lift for Cellana tramoserica exposed to linearly increasing lift forces. Limpet clamping displayed a linear trend (A, y=0.43x-0.16, r2=0.98; B, y=0.39x-0.27, r2=0.95) with respect to lift; however, differences could be observed between limpets (see A and B) both in the slope of the trend and in the degree of variation about the trend line.

View larger version (14K): [in a new window]   Fig. 8. The cumulative probability distribution of shell clamping as a proportion of the lift force for 38 individuals of the limpet Cellana tramoserica. Each limpet consistently clamped at a given proportion of the lift force. The figure shows the variation in the proportional response among individuals. The curve is described by P(x)=exp{–[(a–bx)/(a–bc)]1/b}, where a=0.1241345, b=0.2015748 and c=0.08828305.