The AAAS (American Association for Advancement of Science) Science Journal article can be found here (registration required for the full article).
I have been (un)lucky enough to sight some myself. Just as with coral reef infestations, first you find one:
Then you find blooms of them.
I do not know if these are actually poisonous as many of their aquatic relatives are. In fact I could find little information about them. Local farmers and orchard owners obviously should use caution. Foxes are natural predators of urchins and possibly raccoon-dogs are as well. Perhaps this threat might be a boon for other native wildlife if they are re-introduced to combat the menace.
At Enchanted Learning, I found this diagram of sea urchins.