I saw a one hour documentary about the Okinawa site, Schoch donned scuba gear and inspected the site. He said it was a natural formation and pointed out that there were similar structures on land a short distance away.
He was generous with his closing disposition by saying that humans 'may have tampered' with these natural structures before they went underwater.
In his most recent book (Voyages Of The Pyramid Builders), he said that from what he has seen so far of the underwater structures off the coast of Cuba that they are probably natural structures also.
I just googled images off of your “megalithic remains off Okinawa” and if that guy said the were natural underwater remnants, lol... then he aint got no business in the business!!