A bug sits on the edge of a disk as the disk rotates counterclockwise. Later, the bug starts to move in the direction of the disk's rotation. Does the disk's angular momentum increase, decrease, or stay the same?

4 answers

stay the same. What ever angular momentum the bug gains, the disk loses. Newtons third law.
Wouldn't it be that the disk's momentum is decreasing, but that of the bug-disk system is the same (because the question is asking about the former)?
Yes.
The total angular momentum stays the same, but the bug pushes back on the disk to move forward on it.