Coral Reef Ecosystem: Bleaching & Trophic Cascade Lab (2D)

Environment

Water temperature anomaly +0.5 °C

Nutrient / runoff input 20

Current strength 1.00×

Food Web

Reef sharks (apex predators) 2

Live Readout

Day

Reef health

Live coral cover

Algae cover

Fish population

Bleaching stress

0.00

How it works

Four coupled variables are integrated every frame (Euler steps, sub-stepped for stability), one simulated day roughly every few real seconds:

stress   = 0.9·max(0, T−1)^1.6
dAlgae   = 0.045·N − graze·(1+A/100) − 0.5·C·A/100
dCoral   = 0.6·(1−cor/100)·(1−A/100) − stress − 0.004·A
dFish    = 0.05·F·(1−F/(12+0.5·cor)) − 0.9·S·F/(F+15)
health   = 0.7·cor + 0.3·(100−A) − 10·stress

T = temperature anomaly, N = nutrient input, C = current strength, S = shark count, graze = fish population × 0.006 (herbivorous grazing pressure on algae). Warming bleaches coral directly once the anomaly passes roughly +1 °C; nutrient runoff feeds algae that competes with coral for space; fish graze algae back down but need coral cover to sustain their own carrying capacity; sharks culling the fish population is a top-down trophic cascade — fewer fish means less grazing, more algae, and a slower-recovering reef, even though the sharks never touch the coral directly.

Coral polyps — fade from a healthy multicolour palette to bone-white as bleaching stress accumulates.
Green haze — algae cover; watch it spread when nutrients are high and current is weak.
Fish & sharks — simple flocking sprites whose count tracks the live population and slider directly; sharks chase the nearest shoal.

Bleaching risk: Low

Coral (live) Coral (bleached) Algae Fish Reef shark