Every net-pen cage releases a steady rain of uneaten feed and fish faeces. Each simulated particle spawns at the cage bottom and sinks toward the seafloor at a fixed rate while the current pushes it sideways for the whole descent — so a strong current carries particles far downstream before they land, while a weak current lets them drop almost straight down. Wherever a particle lands, it deposits organic load into a seafloor grid cell; that grid also slowly decays and diffuses over time, mimicking bacterial breakdown and further current-driven dispersal.
driftDistance = currentSpeed × sinkTime
load(cell) += depositPerParticle, decays each frame
severity(cell) = f(accumulated load) → community class
- Stocking density — more fish means more uneaten feed and faeces reaching the bottom every second, raising the total organic input rate.
- Current strength — the same total waste load spread by a strong current covers a wider patch of seafloor at lower concentration per spot (milder, wider footprint); a weak current concentrates it into a small, severely degraded patch directly under the cage.
- Colour scale — teal/green cells still support a diverse community of larger, oxygen-sensitive worms, molluscs and crustaceans; as load rises the seafloor passes through a yellow/orange transitional zone and finally into deep red — organically overloaded, oxygen-depleted sediment dominated by a handful of pollution-tolerant opportunist worm species.
- Peak severity / affected area — track the single worst-hit grid cell and the total seafloor area pushed past the enrichment threshold, the two numbers regulators and farm operators use to judge whether a site's stocking density and local hydrodynamics keep the benthic footprint within an acceptable radius.
Real-world relevance: this is why aquaculture licensing ties permitted stocking density to measured current speed at a site, and why regular benthic sediment surveys directly under and downstream of commercial cages are a standard environmental-monitoring requirement.