Without gravity, there is no buoyancy (nor is any needed).
I guess it depends on what you mean by "needed." If I were
enclosed in a big blob of water in zero g, I'd sorely miss the
gravity that would, in turn, give me net buoyancy (if my lungs
were sufficiently full) and that would, again in turn, send me in
the direction of air, if there were any to be found.