Yes, Amphipods are good little scavengers. There was some people on Reef Central that said that they were eating their zoa's too, but I think was only because they saw them around the Zoanthids also. They usually hide underneath the zoas in the rock crevices. With the zoas disappearing, you can finally see them. If you you still think that you want them reduced in numbers; Six Line and Yellow Coris Wrasses will make a dent of their populations.

-David

http://www.wetwebmedia.com/ZoanthidFAQs2.htm

Amphipod