This worksheet involves a model for a kelp forest with a tipping point that depends on the density of urchins that feed on the kelp. [br][br]The horizontal axis is the kelp biomass in kilograms per square meter of seabed. [br][br]The vertical axis is a flow rate (inflow or outflow of kelp biomass in kilograms per square meter of sea bed per week). The inflow of kelp is growth of existing kelp fronds and establishment of new plants. The outflow of kelp occurs through the shedding of kelp detritus and through grazing by urchins. [br][br]The parameter u is the number of individual urchins per square meter. You can use the slider to adjust the value for u. [br][br]The point A is an equilibrium where the total inflow and total outflow balance. Changing the value of u changes the equilibrium A,.[br][br]If the kelp density is below 5 kg per square meter, the kelp bed is in the collapsed urchin barren state.