Lions will not touch things like urchins, snails, starfish, etc. I dont know what the growth rates of the spiny lobster are, but it should be fine. If you had a 12" lion and a 4" lobster I could definitely see potential problems. Lions swallow their prey whole, but you would be surprised what they can fit in their mouths...I have a radiata lion that swallowed a sally lightfoot crab that was 1/2 its size!
Jon