Susan,
It might be possible to prevent anyone from replying to a post. I would have to investigate the capabilities of this particular message board software tool. But, as Annette points out, it would be difficult to relate comments to an individual APC notice, thus thwarting the fundamental concept and structure of a message board, i.e., various forums, consisting of posts followed by comments, followups, etc. to that post.
If you object to comments being associated with posts, then perhaps you could request that the board post the notices on their own web site. The Costambar forum has no connection to the APC board. If fact, Ann Walsh has been paying the hosting fees herself.