If the volume of seawater increases, or if its mass decreases as it changed state from liquid to solid, then its density must decrease also: less density = ( less mass)/( more volume) Seawater, in fact, undergoes both changes as it freezes.
(its mass; decreases; ) (it; changed; state; from liquid; to solid) (the volume of seawater increases; undergoes; both changes; T:as it freezes) (it; freezes; )
its mass it the volume of seawater increases it
decreases changed undergoes freezes
state from liquid to solid
both changes T:as it freezes