Oyster Reef Boundary Layer: 2D Benthic Depletion Model

The 3D Oyster Reef Filtration Engine tracks a single well-mixed turbidity number for the whole water column above the reef. This 2D companion solves the real advection-diffusion-reaction field instead — concentration varies both along the direction of flow and with depth, because the oysters are benthic and only draw down the thin layer of water immediately above them. The result is a genuine near-bed depletion boundary layer: a real, independently-computed spatial structure (not a flattened 3D scene) that the well-mixed model cannot represent. Raise the current to mix that boundary layer away, or push oyster density up to watch a dense reef starve its own downstream animals of food even while the reef as a whole looks lush.