It looks to be some type of sponge, probably thriving due to excess nutrients. I would just break off what you can, and since many sponges are air sensitive, I would just take the zoos and gsp and sit them out in the air for 10 or so minutes... this wont hurt them at all, as long as they stay damp. I have seen zoos and gsp rocks shipped 24 hours in just wet newspaper many times.