Kelp forests are among the fastest-growing, most productive ecosystems on Earth, but their fate depends on a delicate balance between light, nutrients and grazing pressure. This simulation grows a field of kelp fronds toward the light and lets you push the system toward collapse or recovery.
The Beer-Lambert law of light attenuation with depth, nutrient/temperature-limited growth, and a real ecological phase shift: the collapse of kelp forest into urchin barren when grazing outpaces regrowth.
Adjust water clarity to change how deep light penetrates, tune nutrients to speed or slow growth, and raise urchin grazing pressure until the forest can no longer keep up — then lower it again to watch recovery.
Giant kelp can grow up to half a metre a day under ideal light and nutrient conditions, making it one of the fastest-growing organisms on the planet — yet a single urchin outbreak can strip a forest bare within a season.
This canvas simulation models a vertical slice of a kelp forest, from sunlit surface down to a rocky seafloor. Sunlight intensity is computed with the Beer-Lambert law, I(z) = I₀·e^(−k·z), where the water-clarity coefficient k controls how quickly light fades with depth z. Fifteen to twenty-five kelp fronds are drawn as chains of growing segments; each frond's growth rate each tick depends on the light intensity available at its current tip depth and on a nutrient/temperature multiplier that scales the maximum possible growth rate.
Fronds sway using a sinusoidal horizontal offset that grows with height and animates with simulated time, mimicking the pull of ocean currents. A grazing sea urchin population, drawn near the seafloor and scaled by the urchin-grazing slider, erodes each frond's biomass whenever grazing pressure exceeds the frond's local regrowth rate. Sustained overgrazing causes fronds to shrink and disappear, visually flipping the scene from a lush kelp forest into a barren, rocky urchin barren — a real and well-documented ecological phase shift. Lowering grazing pressure again lets biomass and fronds regrow, illustrating the reversible dynamics (and real-world hysteresis risk) of these ecosystems.
What is the Beer-Lambert law and why does it matter here?
The Beer-Lambert law, I(z) = I₀·e^(−k·z), describes how light intensity decreases exponentially as it passes through an absorbing medium like seawater. In this simulation it sets how much sunlight reaches any given depth, which directly limits how fast kelp fronds at that depth can photosynthesize and grow.
What does the water clarity slider (k) actually control?
It is the extinction coefficient in the Beer-Lambert equation. A low k means clear water where light penetrates deep, letting kelp canopies form far above the seafloor. A high k means turbid or murky water where light fades quickly, starving deeper fronds and limiting maximum kelp height.
How does kelp growth rate get calculated?
Each frond's growth rate each simulated tick is the product of a maximum growth rate (scaled by the nutrient/temperature slider) and the fraction of surface light reaching the frond's current tip depth, computed from the Beer-Lambert law. Fronds near the surface in clear, nutrient-rich water grow fastest; deep fronds in murky water grow slowly or not at all.
An urchin barren is a real marine phase shift where a kelp forest is grazed down to bare rock by an overabundant population of sea urchins, usually after predators like sea otters or sunflower sea stars decline. In the simulation, whenever grazing pressure exceeds a frond's regrowth rate, that frond's biomass decays each tick; if enough fronds collapse the seafloor visually turns from forest to barren rock dotted with urchins.
Yes. In the simulation lowering the urchin grazing slider below the current regrowth rate lets biomass increase again each tick, so fronds regrow from the seafloor upward. Real urchin barrens can also recover, though they sometimes persist for years due to hysteresis — once urchins strip the forest, they can survive on scraps and resist recolonization even if grazing pressure eventually drops.
Water clarity sets the Beer-Lambert extinction coefficient k; nutrients and temperature scale the maximum possible growth rate; urchin grazing sets how fast biomass is consumed and how many urchins are drawn; simulation speed fast-forwards simulated time; and reset restores default values and regrows a fresh forest.
Each frond's horizontal position is offset by a sinusoidal function of its height above the seafloor and of elapsed simulated time, mimicking how real kelp blades bend and ripple under the pull of ocean currents. Taller sections near the canopy sway more than the base near the holdfast, just as in nature.
The Beer-Lambert light attenuation, nutrient/temperature-scaled growth, and grazing-versus-regrowth threshold for the forest-to-barren phase shift are all grounded in real kelp ecology and optics. The frond geometry, sway animation and urchin counts are stylised for clarity rather than a full hydrodynamic or population model.