Energy Balance: Movement

 Houlihan et al. (1985) measured the energetics of swimming for juvenile ($\approx$ 17 g) and medium sized ($\approx$ 42 g) crabs in sea water at 22$^\circ$ C. Base metabolism for these two sizes was $\approx 5.6\times 10^{-4}$ and $2.8\times 10^{-4}$ (g wet wt)/(g wet wt hr). Metabolism increased linearly with increases in swimming speed for both sizes. At 720 m/hr, crabs of both sizes use $\approx$ 5 times as much energy swimming as they do resting.

In the model, the cost of transport per g of body weight depends on the mass, $G$ (g), of the crab and its speed of movement, $v$ (m/hr) (Eqn A.28):

$$= \alpha_{\text{move}}G^{{\beta}_{\text{move}}}\, v$$ (A.48)

where $\beta_{\text{move}} \approx 1/3$ (Houlihan et al. 1985), and $\alpha_{\text{move}} = 0.00004$ (g .m$^{-1}$). The above equation implies that larger crabs use proportionately less energy for movement than smaller crabs (Fig. A10). Under the above parameter values, the ratio of the crab's maximum rate of mass usage due energy expenditure for movement relative to the crab's maximum metabolic rate at $T_{\text{opt met}}=26\ensuremath{^\circ\text{C }}$ is $\approx 3.5$ and the ratio of energy usage for movement plus respiration and excretion to respiration and excretion is $\approx 4.5$, agreeing with the results of Booth and McMahon (1992).