You have two routes that you could choose from:
Take the Studios bus, and then take the boat.
-OR-
Take the MK Boat, and then the Beach Club bus.
If you're trying to get there for a morning breakfast before 9am, I might recommend doing the first... tell the Studios bus driver where you are going, and they might be able to take you directly.
If you're doing this for a late night dinner after both parks have closed, you might need to use DTD as a transfer point.