That is just a harmless pineapple sponge.. they eat silicates from the sandbed and are totally normal.. they will go away as the silica in the SB is consumed..

 

+1

 

It looks like you have two different types of sponges there. As someone else has mentioned one is commonly referred to as a pineapple sponge. The picture is fuzzy, but it looks like you may have a yellow round sponge in front of the pineapple sponge as well. For the most part, sponges are harmless filter feeders, but they do get into chemical warfare with corals in your tank.

There are some articles on the web about this, if you are interested in reading more about it, just search for 'sponge chemical warfare'. As long as your running carbon, there shouldn't be much of an issue.

Basically, because sponges cannot move and lack a hard outer shell for protection, they are highly susceptible to marine predators eating them, such as fish and invertebrates, and in the wild, turtles. Thus, it is not surprising that sponges have evolved a wide suite of defensive chemicals to deter predators from eating them. Also on the reef, space is a limiting factor, so sponges use their defensive chemicals to keep algae from attaching to them and engage in chemical warfare to prevent other species of sponges and corals from growing near them and taking up space that they would want to use to grow.

The reason why I bring all this up is b/c your sponges are very near your mushrooms in the photo. It is possible that they can survive just fine like this, but it is always good to be aware that this unseen chemical warfare is going on as well. Both will continue to struggle for space being so close to each other.

 

It looks like you have two different types of sponges there. As someone else has mentioned one is commonly referred to as a pineapple sponge. The picture is fuzzy, but it looks like you may have a yellow round sponge in front of the pineapple sponge as well. For the most part, sponges are harmless filter feeders, but they do get into chemical warfare with corals in your tank.

No, that is not a sponge. I bought those mushrooms from my local LFS thinking that it was one large rock encrusted with corals, but instead it is a bunch of little rocks - each with a mushroom on it - and these are all held together with a green, hard, foam. So, that sponge is, in fact, foam. Thanks for all the other great information on sponges. I will definitely be googling 'sponge chemical warfare'.

Ratts: Thanks for IDing the pineapple coral. Thanks to that information I googled sponges, and found that my tank has quite a few sponges. Red and yellow slimy looking patches that are also a type of sponge. A closer look at one, and I can see it 'breathing' through a tube like structure.

 

Here's a good article on sponges: http://www.advancedaquarist.com/2011/6/inverts2

 

That is an awesome article thanks for sharing!