Corals host photosynthetic algae (zooxanthellae) that give them color and food. Heat stress makes corals expel these algae — bleaching them white — while lower ocean pH (acidification) weakens their calcium-carbonate skeletons. Both stressors combine with fishing pressure and pollution to reduce the fish population the reef can support.
bleach_risk = clamp(warming/3 + max(0, 8.1−pH)×2, 0, 1)
fish_pop(t+dt) = fish_pop + r·fish_pop·(1 − fish_pop/K) − harvest·dt
K = K₀ · coral_health (reef health sets the fish carrying capacity)
- Sea surface warming — raises bleaching risk and slowly fades coral color toward white.
- Ocean acidification — lower pH values increase bleaching risk and slow coral growth back.
- Overfishing pressure — higher harvest rate directly reduces the swimming fish school size.
- Plastic pollution — adds floating debris particles and a steady drag on the ecosystem score.
Real-world monitoring networks (e.g. NOAA Coral Reef Watch) track exactly these variables — sea surface temperature anomalies and pH — to issue real bleaching-alert warnings for reefs worldwide.