User blog comment:Lord Loss/Monster Hunter Theory... Blog/@comment-6005381-20130519150159/@comment-4009941-20130519155324

If you meant the underwater ruins, Capcom said Abyssal Lagiacrus likes to eat Angler Fish and whale style kinda. You know glow in the dark bait and plenty of plankton. Since we all know whales can survive from that kinda diet and that Abyssal is strong and agile enough to take down large prey when the time comes I beleive it can survive there quite easy.

Oh and its not restricted to living in the ruins, its been known in more ancient times and is recently rediscovered.