Polysiphonia lanosa is a dominant epiphyte on the rockweed Knotted Wrack (Ascophyllum nodosum). I refer to it by its scientific name, because the common name Tube Weed is used for a number of species in the same genera that share its polysiphonous structure, which basically means that with a hand lens it looks like a tuft of tiny connected filamentous tubes1. I see them as the cheerleader of rockweed epiphytes because they look like little brown pom poms, sometimes with hints of maroon or yellow.
1. Gosner, Keneth L. (1978), Peterson Field Guides: Atlantic Seashore – A field guide to sponges, jellyfish, sea urchins, and more