To be honest I am not even sure what coral you focused on. You can up the speed (ISO) and that will allow for a faster shutter speed, and still keep your metering in the middle. Not sure of your F-stop, but you can open up there and also let in light for a faster shutter speed.
Also, often there is a sharpness setting in the camera. Check that out. My 10D always looked soft but looking back it was my settings, not the camera. Additionally, what software are you processing with? I ask because most digital imaging benefits tremendously from processing after taking the image. This includes sharpening (especially if your in the camera settings are low).
One more thing. Are you pressing the shutter manually? If so with this shutter speed you may be inducing movement. Use the timer or a remote release.