I agree with you. I think the "Large Bernacles" are small at the begin and they grow the Bernacle shell shape (witch is the metal-alloy) using the elements they absorb from the nebula. I will compare them to our corals (at lest the red one) there is a little form of life that build a very strong shell around them self.
I will also like to point what for me is one of the very few sure hints we have: They are incredibly strong - much stronger than foamed aluminium for example. Many elements form the structure so technically they are alloys, but the composition is different in different parts of the cell walls for strength. They are good thermal insulators, and have a high melting point, but if they are melted they lose all their special properties and become a conventional alloy
I guess this part is important. They are a kind of alloy with a higher melting point (i assume compare to our common alloy) the most common alloys we know they have a melting point around 1100-1300k. And if we add that they are very good thermal insulator, meaby they have those proprieties to protect the life form inside from high temperature.
Talking about UAs. I think UAs and the Bernacles are 2 different pieces of the same puzzle or completely unreleated. My bet: they are kind of NavBeacon. This will explain why they are all around a shell and they use morse code. My think is that someone like to know who is going around this shell witch the center is Merope (thats simply why they point ther)
Sorry for put more space madness around and my terrible English (Italian here)
Being Italian grants you the rights to have some free REP from me!
That said, I totally agree with your thoughts as well.
Few but Good, I may say...