Model-calculated evolution of O2 concentration near WSI and burrow wall during each rest–ventilation cycle of N. diversicolor (9.3 min). The relief in these mesh diagrams indicates the concentrations and gradients. At the beginning of each rest period (T1 = 0 min), the burrow water is fully oxygenated. It becomes less oxygenated during the rest period, as seen at halfway into the rest period (T2 = 2.3 min) and at end of the rest period (T3 = 4.6 min). Immediately following, the macrofauna begins ventilation (T4 = 4.6 + Δ min; Δ is equal to one time step in the model run, which is 8 in these simulations) resulting in the maintenance of the burrow water O2 level, as seen at halfway into the ventilation period (T5 = 6.9 min) and at the end of each rest–ventilation cycle (T6 = 9.3 min).