Growth and Molting

Except for the qualitative description in Appendix A.5.11 (which we will not repeat here) few quantitative criteria can be specified to assess the model's rates of crab growth. Crab growth is the result of interaction between rules governing crab feeding, energy balance, metabolism, molting and environmental conditions. 7th instar model crabs were typically instantiated in early August and reached instar 12 by early September, although many did not reach this stage till the following April. A model crab's energetics were such that 1 gram of food intake (with an average food quality of $\approx$ 400 cal/g) was required for a crab to gain $\approx 0.15$ g of mass. Molting generally ceased during November to April, although a few of the larger crabs (instar 19 & 20) molted during March (Fig. B6). Cessation of molting during winter results in two distinct relationships between CW versus intermolt period (Fig. B7), and age versus CW (Fig. B8). A 15 instar crab added $\approx 15$ g between molts, while an 18th instar crab added $\approx 50$ g. A 10 cm CW crab added between 1.5 and 1.8 cm to its CW when it molted. The empirical cumulative distribution function for the time to sexual maturity indicated it took approximately 1 year for a crab to go from the 7th to 18th instar (Fig. D5). Crabs reaching the 18th instar did so over a range of months (typically June to October, Fig. B9). At temperatures between 22 and 30 $\ensuremath{^\circ\text{C }}$ molting took between 24 and 44 hours (Fig. B10). Crabs generally spent $\ll$ 5 hours continuously foraging during summer and went through long periods ($>50$ hours) during October through April when they did not eat because of their low metabolic rate.