What were the conditions like when you took the shot?
It looks like it was a fairly dark scene with the sun hitting the top of the coral. The exposure meter on your camera sacrificed the highlights so the rest of the shot wouldn't be completely black.
If you wanted the rest to be dark, you could point the camera at the part where the sun's hitting (or something of similar color, but fill the frame), push the shutter half-way, hold it, frame the shot like you want it, then push the shutter button the rest of the way down. -That'll make the camera expose for the highlighted area, but be careful with focus because that's set when you push the shutter halfway as well.
I have a Canon SLR for on-land photography and I didn't know how spoiled I was by it's autofocus and auto-exposure until I got a cheapo Olympus to try out UW photography with. I've been using the Oly on land for a few months to get used to it before my trip (in two weeks!), it's frustrating, but I'm getting the hang of "fooling" it so a picture comes out like I want.
For the record, my fiance's Nikon Coolpix 2000 is much more foolproof (better at focusing and exposure) than my Oly C-5000. Although I am proud of
this shot taken with the Olympus. -It can be done, it just takes some practice.
