Hey, even without the external flash, you can shoot macro all day long! I use a cheap Olympus c-4000 or c-750 with an underwater housing and (occasionally) a sea and sea ys-30 strobe.
Seriously, though, you guys have WAAAAAY clearer water down there than we have here, I would think natural light (down to 25-30 feet or so) would be enough to aid the built in flash. Here's a couple I took in puerto rico a few months ago with NO external flash....
Flamingo Tongue Cyphoma
Conch and Juvie Bluehead wrasse
Grunts and Squirrelfish
Lettuce Sea slug
Pederson's Cleaning Shrimp
I love Conch.
Boring Urchins
upsidedown Jelly
Wicked Trumpetfish
Wookie Crab (we call them that, they are actually in the genus Mithrax)
Cheers,
Kat