A single colony accretes polyp by polyp across simulated centuries. Warm the lagoon and watch it blanch — honestly. Cool it, and the algae come home.
Each polyp lays down a fleck of calcium carbonate and buds the next. The branching you see is an L-system running in slow motion — thousands of tiny masons, all descended from one larva that settled on bare rock.
Coral tissue is nearly clear. Its gold comes from zooxanthellae — algae boarding inside the polyps, trading sugar for shelter. In the model, that gold is a rented pigment. When the rent stops, it leaves.
Push past roughly 29.5 °C and the polyps expel their algae — you'll see gold motes drift off and the reef go bone-white. It isn't dead yet. Cool the water and the tissue reseeds. Hold the heat, and it won't.
A reef spends three centuries building — and can unbuild in a single hot summer.
The colony is not a texture or a looped video. It is an agent simulation: branches with living tips that deposit skeleton, bud daughter branches, and carry a per-segment count of symbiotic algae. Temperature drives that count up or down.
Tips bleach first — they're the most exposed — so blanching spreads inward exactly as it does on a real fringing reef. Recovery is deliberately slow and asymmetric: pigment leaves in days and returns over seasons.