You're right. If displacements are added, it would be 1+0.5 though.
I wondered about the transparency above 1, and indeed it is not 100%. Pulling it even higher has some strange effects, interesting.
I made a comment about color disabling in default shader somewhere too, would indeed be very handy (if translucency would then still work in water shader).
Turning off shadows of the sharks was the easiest way to get rid of the grain, btw.