Something to do with ammonia in nebulae ?
Going back to my (extended) hypothesis
large barnacle -> release UA seed pod -> release spores -> grows in to barnacle spike -> grows in to large barnacle.
If this is the case then in order for the UA seed pods to get where they are they need a lot of energy to get them to where they are now. They would have to travel faster than light which implies some sort of frame shift. This could either occur within the UA (there is evidence of some odd distortion when they expire) or within the large barnacle. If in the large barnacle, the process would probably destroy it when the energy is released to propel the seeds to their destination.
Our FSD drives need hydrogen to provide the power and one of the main constituents of nebulae is hydrogen.
Anywhere too close to a star would be too hot for meta alloys to survive, but in a suitable spot in a nebula on a planet without an atmosphere, but with enough gravity to pull in hydrogen it could possibly be harvested. It would probably take a long time before sufficient is available eject pods.
Thinking about the UA behavior they could be looking for a mate from a different barnacle source before releasing mature spores. Taking one into a ship might prematurely trigger the spore process.
All this is pure speculation