Creature From the Deep: If Manphibian begins the turn occupying water terrain, modify his speed and attack values by +2.

How long do these modifiers last? Does Manphibian have to stay in the water terrain to keep the bonus during the turn?
You check for the water terrain at the beginning of each turn. If he occupies water at the beginning of that turn, he gets the modifers for that turn, and he does not need to remain in the water to keep them that turn. If he doesn't, then he doesn't get any modifiers that turn.