sandbed critters

[Jack]

Ok, I cycled my live rock about a month ago in my tank, I haven't gotten my sand for my DSB yet and I was wondering where do the little sandbed critters come from? I guess they jump off the rock(?), but the thing I am wondering is if I don't have the right substrate in there now, will they survive? I have large crushed coral 2-4mm in there right now. Will I have to get some sand from an established tank to "seed" my sandbed? Thanks :D