How can Mera, Vulko and Atlanna breathe air while other Atlantians can't?

Did you not see BvS? PiS is a staple of the DCEU.

Comicbook speak. There are three levels of screw-ups to further a story once you get yourself into a corner: CiS is character-induced stupidity. When a character does something so out of character, but he has to do it for the story to work, like when Superman agrees that his father dying in a tornado is better than explaining to 8 people in an underpass why they can’t tell anyone what happened.

Now WiS is when the writer specifically (or director in movie cases, maybe ‘creator’ is best term) goes away from his traditional story telling methods to essentially make a brain fart he could have easily worked himself around. An example of this may be when Christopher Nolan essentially embraced shoddy, even ghastly fight choreography in his second and third Batman films when there really isn’t any viable explanation as to why he’d okay this. Lack of budget? No time to fix it? Unlikely. Or maybe when they used the Knightmare scene in BvS with no intended payoff... but I guess we could create a sub-category of Producer-induced stupidity? But all the same.

Finally, we have PiS, plot-induced stupidity. Not specifically connected to characterization and more poignant to the story than simple WiS (which technically everything is, but the differentiation is more to what type of WiS it is), this one involves a scenario where something has to happen for the story to continue, whether it be a flat out plot hole, or just dumb as hell. For instance, what exactly was the plan with Doomsday if Batman killed Superman with the Kryptonite Lex knew Batman had? The idea from the writer/director was that it doesn’t really matter. Whether or not that’s acceptable, it is PiS. Some people can inexplicably breathe out of water when it’s explained their species isn’t able to? PiS.

More for comic book debating, like “can anyone explain why Superman is pulling a planet in this panel but can’t punch through a steel wall in this one?!” Because the plot demands it.

It's true that they didn't get into "how". But Mera does mention it in the movie. So Its not an oversight or an error. Something about the royal lineage being able to I think she said?

Yeah they said in the movie that those who were High Born could breathe on land and in the water.

So this thread is more a result of someone's ignorance instead of an actual error. Cool.

No you don't.

They can give an explanations as to why something is and still have it as PiS. If one group can breathe in a specific atmosphere and another group can’t, they’re not different aristocracies, they’re a different species altogether. They’re as different from Atlantean as Atlanteans are from humans.

Well, Aquaman is half human... can't speak for the rest of the gang.