Actually it's their volume.
If you place the same size ball in a predetermined amount of water, one being a marble the other made of steel (weight being different) the displacement remains the same. Now increase the size of the marble proportionally until the weight is the same as the steel ball (it would be 4-5 times are large now) and place it in the same amount of water, the displacement is MUCH larger.
After all these years, grade school science still sticks.
Originally Posted by HN1
Water displacement after the rock will only be due to submerged equipment, corals, fish etc. Anything not water placed into water will displace water. The amount is determined by the weight of the objects, not their area.