Here's a partial article from Coastal Fisherman:

Sea Urchins
"Sea urchins are another great live bait choice in the summer for sheepshead. Like fiddler crabs, sea urchins are one of the main food sources for sheepshead. That’s because sea urchins live on rock jetties and any kind of pilings they can attach to. Sea urchins are very intimidating to most people because they are so crazy looking, with a small round body with spines everywhere. They kind of look like a saltwater porcupine. But, don’t fear, they cannot shoot their spines into you. Yes, if you just grab one without being gentle, you can stick one into you. Just pay attention of what you are doing and you will be fine. Before you put them on a hook you want to cut all the spines off, so you are left just with the main body. Doing this makes it a really easy meal for the sheepshead, they just cannot resist this bait. It’s like cutting up the food for them and hand-feeding them. To keep them alive all you need is a bucket or a livewell with saltwater and they will be fine. Again, the best rig to use with sea urchins is a Carolina rig. The hook size varies from a # 2/0 to a # 7/0; some anglers like the smaller size and some like the large size. While all sizes work, Gamakatsu or Owner hooks are the best because they are so sharp. You need to use a super sharp hook with sea urchins because your hook has to penetrate their hard body."

I used to use them in Jacksonville Beach and Mayport for sheepshead and did just fine with them. They stay alive in a bait bucket for days if kept in moving saltwater.


  

In the rocks, on pilings, and on some seawalls. Hook them through the body (through the shell) with a SHARP hook after you cut off the spines with kitchen shears.