You may have inadvertently multiplied -- exponentially -- the number of urchins that you "smashed." Urchins, among other echinoderms, broadcast-spawn sperm and eggs, to reproduce -- especially under stress; and urchins are little more than gonadal tissue, with a tiny animal, added almost as an afterthought.
Jostle a catch bag of urchins and you'll quickly notice a white discharge on the aboral surface (opposite the mouth) of many, which then spreads like a chain reaction = "happy ending" of both eggs and sperm.
Under laboratory conditions, while working at bioassay labs, we either injected them with KCl or outright smashed them to spawn -- and smashing always worked, even out of season; and we had tens of thousands of fertilized ova within days -- pluteus larva, the final stage, just before spines develop, within four weeks or less.
The only safe way of eliminating them is physical removal, which the pencil-necks at Fish and Game don't seem to appreciate.
It also recalls the lamentable efforts in Oz, to eliminate the "crown of thorn" starfish (Acanthaster planci), decades ago, by cutting them into pieces, without giving thought that each segment would simply regenerate an entire sea star . . .
