oh btw, I also posted this question on the RC S. FLA forum figuring that mangrove fuges may be a little more common down here...here is what one guy had to say about it...
"Live rock will do significantly more denitrating than anything else, and the whole idea of using the skimmer is to remove organics before they have the chance to break down into ammonia->nitrite->nitrate. A mangrove might take up a small ammount of nitrates and phosphates, but does not remove the organics from the water, if anything else it'll add more organics. Also you can absolutely kill any plant matter (mangroves included) if you try to introduce them to a high nitrate level tank. They can only stand levels up to 50ppm or so (I read all this somewhere... probably advanced aquarist or something? I'd look it up but I'm scraping my time together just to be on our forums. I'm sure work doesn't look favorably on surfing the net all day). If the nitrates rise too quickly, they'll shut down and will not reduce nitrates, and will die off, increasing ammonia->etc->etc.
People think that a skimmer reduces nitrates. It does not. It simply removes organics before they can process through the nitrogen cycle into nitrate. A mangrove will absorb a tiny bit of the end of the nitrogen cycle, and a BIG maybe on the idea that maybe it's own surface area can keep a small population of aerobic nitrogen reducer microbes on it, but not likely, and not in significant enough quantity to make a difference really."
