They will move/spawn/split whatever they want to do really. You can pull him off and put him where you want, this is tricky with shrums though, they shrink up to nothing when you handle them and are slimmy as can be but you can do it with a thread needle and som fishing line. just poke it through the base and tie him where you want... or... you can leave him to do his business, the problem with that is you may not see him ever again because the current will probably take him to a dead spot under or behind your LR and there when he stops moving he will attach.
Cheers
