Background Prey

Background prey is a potential food source for crabs that cannot find sufficient clams. Background prey represents an aggregate of different possible crab prey (other benthic species, dead organisms, etc.) and is modeled at the scale of the finest triangles using a modified logistic growth model. Let $N$ denote the number of grams of background biomass on a given triangle with area $A$ (m$^2$). Changes in $N$ (g) occur according to:

$$\Delta N = \left(1 - \frac{N/A}{K}\right)\, r_{N}\, f_b \, \tilde{N}A \Delta t - \alpha N \Delta t - - .$$ (A.25)

As with clams, this prey is updated every 24 hours ($\Delta t$) and its growth rate depends on temperature and also DO via $f_b = f_$c$\left(T;\beta_{\text{b,grow}}=0.2, T_{\text{b,max grow}} = 35, T_{\text{b,opt grow}}=26 \right)$ (Eqn A.18). $r_N$ = 0.0008 (1/hr) and controls the maximum rate of growth. $K=400$ (g/m$^2$) is the carrying capacity for background prey on a triangle while $\tilde{N}$ (g/m$^2$) is the average density of the background prey calculated over the current triangle and its immediate neighbors and enables some spreading of background from patches of high density to low density. Background prey on each triangle experiences mortality due to other predators not included in this model at a rate governed by $\alpha$ = 0.0002 (1/hr). Mortality due to hypoxia is calculated using Eqn (A.21) with the same parameters as for clams. The last term in Eqn (A.25) accounts for the number of grams consumed by the crabs over $\Delta t$ (Appendix A.5.2).