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Journal of Experimental Biology 113,55-68 (1984)
Published by Company of Biologists 1984

Analysis of the Scaphognathite Ventilatory Pump in the Shore Crab Carcinus Maenas : I. WORK AND POWER

A. JOFFRE MERCIER ¹ and JERREL L. WILKENS ²

¹ Department of Biology, University of Calgary, Calgary, Alberta,T2N 1N4, Canada; Department of Zoology, University of Iowa Iowa City, Iowa 52242, U.S.A.
² Department of Biology, University of Calgary Calgary, Alberta, T2N 1N4, Canada

Measurements of branchial pressure and ventilation volumes were used to calculate the work and power of gill ventilation in Carcinus maenas, during spontaneous as well as forced unilateral ventilation. With increasing ventilation rate (fR), the stroke work increases as a result of an elevated gradient of branchial pressure, while power output increases as a result of enhancement of both the pressure gradient and the flow rate. To a first approximation, the stroke work is proportional to fR^1.5, and the power out-put is proportional to fR^2.5. The available evidence suggests that flow is mainly laminar through the branchial chamber but turbulent through the pumping chamber. Evidence is presented which suggests that the crab is able to vary the resistance to the flow of branchial water.

The increased branchial pressure at elevated ventilation rates constitutes an increased load on the ventilatory muscles. Measurements of isometric tension confirm that the muscles compensate for this increased load by generating greater force. Electromyograms support the notion that the change in force results from appropriate changes in the output from the central pattern generator.

Key words: Ventilation, work, power

Accepted on February 17, 1984

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