It is a good start. Nice composition in several of the pictures.
One thing that often helps is, whenever possible, get slightly below your subject and shoot upwards. You'll get a rich blue background instead of sand or rocks.
Also, get as close as you possibly can. For instance, in the last picture the grunts aren't entirely clear and sharp because of the amount of water between them and the camera. By moving slowly, you should be able to get within 2 feet of fish like that. Then zoom the camera all the way out, and you'll get a better looking picture.
For the wreck shots you would need a wide angle lens to get closer. But if you positioned your model in the 2nd shot just in front of the wreck instead of behind it, at least they would be clearer.
The C-5050 has raw mode capabilities. If you've got a large enough memory card, then always shoot in raw mode. You can then adjust the white balance afterwards to avoid the blue tint on your pictures, as well as making minor adjustments on exposure.
If you don't have enough memory to shoot raw mode (each image takes 7Meg) then use manual white balance.
-Mark