You all seem to have a lot of sea urchins in So. Cal. Do they not have a natural predator? Wouldn't there be a great commercial market for uni, or are these not edible? I saw two kinds when I was there, light purple smallish ones and dark red wine colored larger ones. The larger dark ones seemed to hide in cracks (or create their own holes it seemed) and the light purple ones were everywhere. Wondering why we have some in Monterey but not a great abundance, sea otters eating ours, perhaps?
When you go to a protected area, like parts of Anacapa (protected = no fishing) the larger predators that eat urchins, Sheephead and Lobster, I believe, thrive and mow these things.
When you fish without discrimination, like, say, the Coronados or parts of Catalina, or parts of Anacapa, all of the urchin eaters are gone.
So urchins thrive. Especially the purps.
Urchins eat kelp holdfasts. So the Kelp is gone.
So you have acres (or miles) or urchin barren.
In move the brittle stars.
So you get acres (or miles) of creepy gold shag carpet.
Its not pretty. All you need to do is spend a day on Anacapa, do a couple of dives on each side of the island and you get a great idea of what kind of remarkable impact protecting these large predators from over fishing can have on a system. On one side you get creepy gold shag carpet, the other side you get lush kelp, abalone, lobsters, large fish in abundance, and clearer water.
So yeah - we have too many urchins.
In some places.
In other places, like these protected areas, we don't have too many urchins - we have just the right amount of urchins.
You don't need to look any further than Marineland in SoCal. The Bay folks pull out zillions (and I mean many, many thousands) of urchins from this very fished spot, and they seed kelp. The kelp thrives - even in this very fished place, but only because of the emergency urchin relocation program (EURP).

If the urchins were left to do what they do in this very fished spot (read: no large sheephead, no large lobster, no real urchin eaters), it would look today like it did 4 years ago - an urchin-barren, kelpless pile of rocks.
So yeah - we got urchins.
But you have wolf eels. So there.
You have less fishing, better fishing regulations, more protected coastline, more non-commercially fished species that eat urchins (like the wolfies) and so your urchins are kept in check.
-Ken