The Aquantis have tunnled under Crystal Island and emreged near Crystal Guard III. He explains to you that he can't slay the beasts and guard his current position at the same time, and asks if you can kill 6 Aquantis Invaders for him.
After taking care of the invading Aquantis, you speak with Crystal Guard II, who says you can help make it easier to camp in the valley at night. She is vague as to what this help might entail.