THe number of mega pixels is the least thing you should be worried about.
"Panasonic - Lumix 8.1-Megapixel Digital Camera 10x optical zoom 299.99" tells us nothing.
"Panasonic - Lumix DMC-LX3" tells us everything.
In a reef you want the following qualities paramount over all others:
1) The ability to shoot RAW
2) A manual transmission. IMO Automatic cameras are all but useless in reef photography. The ability to select your Shutter Speed, Aperture, and ISO speeds independently of eachother will take you far. Of course you have to know how to drive a stick shift if you want to make use of buying one.
3) lens quality, loosely f/2.8 is better than f/3.5.
4) Minimum focus distance. The shorter the better.
There are a lot of other qualities but this is what I would look for first and foremost. Megapixels don't make the list...but shoot for at least 7. Seven mega pixels is as good as ten megapixels.