They will eventually destroy everything. Though they are safe as far as eating coral, they will knock them over and will eat any other shrimps or clams that they can get a hold of. By the way, most species of spiny lobsters are illegal to keep unless they are of legal size to collect both in FL and CA. There is a specie from CA that does not do well in trop tanks, it is collected in southern CA, not sure what sp is in the store you are talking about, but there is a spiny from FL called a spotted or spanish lobster that has no size limits and is quite attractive, it is black with numerous white and red spots all over the body and tail, it does get big though, and will knock everything over and eat most other inverts.