Submerged habitats are very unlikely to be a thing. Though humans have lived ON water for a long time in large numbers. There are many people living in boats and barges, veritable citys in south asia, and other areas. Submerged structures will suffer from hugely expensive engineering and construction costs, and you dont have to go very deep at all, before the pressure differential is greater than in space. Salt, corrosion, maintenance, wildly complicated and expensive.Air handling will be very loud, and prone to failures, water and waste, will also be extra complicated, leaks will be profoundly unpleasant.If we are talking about high end resort or theme hotels, then , whatever. On the other hand Mega floating and semi submerged structures can be built from any and all materials, and the engineering is strait forward. Still there is a vast amount of barren and waste land ,that can be utilised at much less effort, so none of it makes sense, except situationaly.... Singapor, and such.

"Sure, it ain't one of them la-de-da above-ground places,

but if you like dank... forget about it."

Would you kindly come settle in Rapture?

But what colour the bike shed?

We are so far away from living independently underwater that I'd say we're hundreds of years away, if it's possible at all.

Energy production. Food, water, air. Resources. Mining. Industry. The harsh environment (salt water, fouling et al.) Even "gravity" (as in, if you drop something underwater, some of it goes up ...)

>> Who made any claims of self-sustaining?

No one in the article. But it has come up in the comments of previous articles (and I see in this thread as well.)

Life on land is self sustaining. Not in the "we don't need oceans" sense, but in the "we don't need people living in the oceans" sense. Conversely to live in the ocean we (currently) must have people living on land.

How would humans make Earth less habitable than Mars?