Giant kelp (Macrocystis pyrifera) can grow over 30cm a day, building towering underwater canopies that shelter fish, otters and thousands of other species. But kelp forests are fragile: they depend on cold, nutrient-rich water and on predators keeping sea urchin grazers in check. Remove the predators or warm the water, and urchins can graze a lush forest down to bare rock — a stable alternate state called an urchin barren.
Sea otters are a keystone predator of urchins along the Pacific coast — where otter populations collapsed from historical hunting, urchin barrens spread; where otters recovered, kelp forests often did too.
An interactive 3D underwater kelp forest: adjust nutrient supply, sea urchin population and water temperature to watch a lush kelp canopy grow, thin under grazing pressure, or collapse into a bare urchin barren.
Kelp growth depends on nutrients and cold water, while sea urchin grazing removes kelp tissue. When grazing outpaces growth, kelp cover collapses and can settle into a self-sustaining urchin barren — a classic ecological tipping point.
Raise nutrients and lower temperature to help the forest grow. Increase the urchin population or raise the temperature to trigger thinning and collapse. Watch the canopy-cover and ecosystem-state readouts update live.
Sea otters, a keystone predator of urchins, help keep Pacific kelp forests healthy — where otters vanished from overhunting, urchin barrens spread across huge stretches of coastline.