Some types of sponges will often grow on the bottom of the rock out of direct light.Other types,will grow in full sunlight.It really depends on what kind of sponge.I have seen a certain type of hitchiker sponge wither away when moved so it was getting direct light.I've also had different types that didn't seem to mind.
Sponges are filter feeders and most of the ones you buy from the LFS generally waste away