BURROW VENTILATION IN THE TUBE-DWELLING SHRIMP CALLIANASSA-SUBTERRANEA (DECAPODA, THALASSINIDEA) - III - HYDRODYNAMIC MODELING AND THE ENERGETICS OF PLEOPOD PUMPING

The process of flow generation with metachronally beating pleopods in a tubiform burrow was studied by designing a hydrodynamic model based on a thrust-drag force balance. The drag of the tube (including the sh rimp) comprises components for accelerating the water into the tube en trance, for adjusting a parabolic velocity profile, for accelerating t he flow into a constriction due to the shrimp's body and another const riction due to the extended tail-fan, for shear due to separation and for the viscous resistance of all tube parts. The thrust produced by t he beating pleopods comprises components for the drag-based thrust and for the added-mass-based thrust. The beating pleopods are approximate d by oscillating flat plates with a different area and camber during t he power stroke and the recovery stroke and with a phase shift between adjacent pleopod pairs. The added mass is shed during the second half of the power stroke and is minimized during the recovery stroke. A fo rce balance between the pleopod thrust and the tube drag is effected b y calculating the mean thrust during one beat cycle at a certain flow velocity in the tube and comparing it with the drag of the tube at tha t flow velocity. The energetics of the tube and the pump are derived f rom the forces, and the mechanical efficiency of the system is the rat io of these two. Adjusted to standard Callianassa subterranea values, the model predicts a mean flow velocity in the tube of 1.8 mm s(-1). T he mean thrust force, equalling the drag, is 36.8 mu N, the work done by the pleopod pump per beat cycle is 0.91 mu J and the energy dissipa ted by the lube system is 0.066 mu J per cycle. The mechanical efficie ncy is therefore 7.3%, Pump characteristics that may be varied by the shrimp are the beat frequency, the phase shift, the amplitude and the difference in pleopod area between the power and recovery strokes. The se parameters are varied in the model to evaluate their effects. Furth ermore, the moment of added mass shedding, the distance between adjace nt pleopods, the number of pleopods and the total tube drag were also varied to evaluate their effects.