Except for macro, the original lens list at the beginning of the thread is a poor choice underwater. If scenic shots are what you want, reefs, wrecks or divers, then you have to look at wider lenses.
The love-hate divide around the Nikon 12-24mm is documented all over the web, but everyone who uses it loves the 10.5mm. One money-saving option is to buy a Magic filter and not a second strobe, and use the 10.5mm in ambient light down to 45-50 feet.
The port is another issue, but having a DSLR with only a flat port makes no sense, unless you are absurdly fond of close-up and macro images. Underwater photographers love macro images, but the rest of the world seems to prefer scenic wide-angles.
A used 16mm is an option, with about 90 degrees of coverage, but the lens seems less forgiving of dome choice, and has a funny optical arrangement with a rear filter that seems optically necessary on the surface, but only with some domes underwater: I've tried it with focussing problems on some occasions. The big advantage is that DSLR users are sometimes selling this lens on and buying the 10.5mm.
Tim
B)