So you dont think it would attack/kill off the chaeto macroalgae? What about other life that may come with/live in it eg. copepods, amphipods, bristleworms or starfish etc?
I doubt very much that it would eat the chaetomorpha. It would scavenge for food. It might land itself amphipods in the chaeto, but I find it unlikely it would manage to catch cocepods because they are pretty quick and only about 1.5mm in size.