We have similar problems in places here in New Zealand urchin barrens are taking over from kelp - here it's thought to be caused by over fishing taking out the

We have similar problems in places here in New Zealand urchin barrens are taking over from kelp - here it's thought to be caused by over fishing taking out the larger/older fish that previously kept the urchins (kina) under control. Kina are considered a delicacy here, but as mentioned here the kina in the barrens are underfed and not worth eating