8 Oct 2014
A much-weathered limpet with barnacles, knotted wrack and Polysiphonia lanosa.
And here's some Ascophyllum nodosum (knotted wrack) almost completely buried in the red epiphytic seaweed P. lanosa. The Ascophyllum has pushed a receptacle (the reproductive part of this sexually reproducing seaweed, which contains the conceptacles, the gamete producing organs) out through the mat of P. lanosa that completely coated its fronds:
It has been thought that the red P. lanosa was a pure epiphyte; that it just used the bigger Ascophyllum as a convenient place to grow. Research (from the American Journal of Botany) has demonstrated a two-way exchange of photosynthesis-derived compounds between the larger Ascophyllum and the epiphiytic P. lanosa.
So the small red P. lanosa gets both a substrate to grow on and some nutritional benefit from Ascophyllum. It's a hemiparasite rather than a simple epiphyte. I wonder what benefit the larger Ascophyllum gains from having P. lanosa grow all over it.