Healthy colony
Bleached (symbionts expelled)
Dead / algae turf
Reef health & heat-stress history
This companion simulator replaces decorative fish-and-coral scenery with an actual ecological mechanic: a grid of coral colonies, each carrying its own genetic heat tolerance, individually tracks accumulated thermal stress the way marine scientists do — as Degree Heating Weeks, a trailing twelve-week sum of how far sea temperature sits above each colony's bleaching threshold. Push the temperature slider past a colony's threshold and its zooxanthellae (the symbiotic algae that give coral its color and much of its energy) are expelled over the following simulated weeks, draining the colony from vivid color toward bone white — real bleaching, not just a color animation. Lower the pH slider to model ocean acidification and the same temperature rise becomes more dangerous: acidification compounds thermal stress and slows recovery, so colonies that would have survived a heat wave at pre-industrial pH can die at today's pH. Colonies that stay symbiont-starved for too many consecutive weeks cross into permanent mortality and are overgrown by algae turf, while colonies that get relief before that point slowly regain their color. The live chart tracks reef-wide health percentage against the accumulating heat-stress signal so the delayed, threshold-driven nature of a real bleaching event is visible rather than instantaneous.