[ And he's all too happy to provide it, especially when it's of such a harmless nature. Anyone with a basic understanding of engineering could come up with the numbers, he just happened to be the one who did the work. ]
From an engineering standpoint the dome itself needs to be heavily fortified just to withstand the pressure at this depth — we're talking about a tons worth on every square inch, or 2400 psi. The shape certainly helps too, but I don't know... if they do decide to attack, I'm not sure it would be able to hold for the added pressure.
As for the creatures themselves, I haven't been able to get a good enough look but something that massive living at this depth..? It doesn't make any sense.