I wintersowed various OP tomato seeds (Thanks, Trudi!) and transplanted them to containers with slightly old potting soil amended with manure and blood & bone meals, fed them seaweed/fish fertilizer, and they were happy enough that I took off their waterbottle hotcaps last weekend.

This Saturday I topped them off with a couple of inches of new MG organic potting mix (so the stems could grow more roots), and I didn't replace the hotcaps. Only about one or two sets of true leaves were above ground, so I probably should have.

The next day I checked on them, and 7 of the 9 plants had been bitten off at or near the growing tips, which I assume means they're goners. The remaining little stems are solid and healthy-looking, not wilted.

Could I have introduced pests via the MG organic potting mix? Are rats or mice (urban rooftop garden) possible?

At this point, I want to buy seedlings and get them going ASAP, but not if they're going to be chomped down again.

Sorry I don't have pix. All advice appreciated.

I seriously doubt it.

You asked "Are rats or mice (urban rooftop garden) possible?"

I wouldn't think so.

Birds fly. Birds like fresh greens.

Whether they'll survive depends upon if how much of the top is gone. You said "bitten off at or near the growing tips." So I would assume they still have one or more leaves. Right?

Some still have one or more leaves, some don't. I cross-posted this to the tomato forum, and got an encouraging reply that (with one leaf left) a new growing point generated within 2-3 weeks. So I might try to leave the more hopeful-looking plants and see what happens.