I remeber this question was asked before but never answered.
To put the secret to rest, here's a screenshot of the map opened in the editor:
Because "warp" nodes show up as a circle on the minimap, you've got this artifact left there. There's a bunch of unused warps, and also a few unused maps in the game. Sadly, they are unfinished, but they give an interesting insight in the development process and scrapped ideas. Kelp forest was originally much larger. And there is another Mithalas map where you could sacrifice victims to mithala, for example. I bet it had something to do with the priests.
If you're interested, use a dev version to be able to use the editor everywhere, not only in mods.
