Moral Vacuum
This movie contains a strange moral vacuum. The Captain risks not only his own life, but his ship, crew and passengers' lives to make enough money to retire on. When the crew rebels, he is prepared to kill to stop them. And when they take to the lifeboat, he does shoot the radioman.
In fact, the first officer and those members of the crew are almost the only moral people in the story. When they depart, we can only presume that they are killed by the storm. The girl from the Lost Continent also displays some morality, but she ultimately plays only a small part in the story -- to the point that at the end, the ship apparently abandons those shipwrecked people in its haste to get away from the Sargasso. But everyone else is morally compromised in some way. That's why they're on this ship. You might think then, that this voyage is about their salvation. But you'd be wrong.
The Captain's immorality is paralleled by the Spaniards; they're quite prepared to kill anyone who gets in their way in order to get what they want. So it seems odd that it isn't the Captain taken prisoner and forced to face his true predatory nature, but a minor supporting character, the engineman. The Captain not only bursts in like a hero, throwing Phos B bombs and shooting Spaniards, but at the very end he's quoting the bible like he's the moral authority of the movie and not a moral vacuum. If they were trying to signal his hypocrisy here, then they succeeded -- but the rest of movie plays it straight, so I doubt this interpretation.
So we never learn that the Captain's changed from this experience. Of the passengers, only the drunken piano player changes when he gives up drinking. The movie seems to go out of its way to prevent the characters from growing. Just as it refuses to put the captain (ostensibly the main character) in a position where he can face his shortcomings, it fails to put the mother who stole $2 mil to recover her lost son with the only boy in the story (el Supremo) where it might trigger some emotional growth. We see her at the end holding his dead body, but the story is over: it's too late and it means nothing.
Is that the ultimate message of The Lost Continent: life sucks, people suck, and it just goes on?