I got a bunch of corals from someone who was breaking down there tank. One of the rocks had some zoanthids and a black sponge mat. They said it had grown in their tank for a long time and didn't cause any issues. As you can see in the pictures, it is starting to grow around the zoas and it is even spreading to a another rock. Seems easy like I can take the rock and peal it off if I want to get rid of it or I can break the rock to separate the zoas and put the sponge somewhere else in the tank where it won't spread. Any thoughts on what sponge this is? It looks like black velvet maybe (https://www.aquaculturenurseryfarms.com/live-sponges/black-velvet/). Is this something I should try to completely remove from the tank?
Thanks in advance.