The sea urchins then overexploited their main food source, kelp, creating urchin barrens where no life exists. No longer having food to eat, the sea urchins populations became locally extinct as well.
The sea urchins' overconsumption of kelp led to the creation of barren areas devoid of life. This, in turn, caused the sea urchin populations to dwindle and eventually become locally extinct due to lack of food.