What do yougrow or hunt there?
There's a reference somewhere in the book to cutting something up "like a fresh bat," which led me to believe that Ketrans might eat some nature of batlike creature (equivalent enough to a bat, at least, that their word for it would be translated to our word 'bat').
It is also said that the Ketrans gain energy and sustenance from the crystal itself. Perhaps the crystals are actually in some way alive (and this might also explain how they can grow without being submerged in a mineral solution, which earth crystals require for growth), and can photosynthesize much like plants on earth do, and Ketrans eat them, possibly supplementing their diet with other creatures (like bats) which might also eat the crystals.
