They leave small round structures called 'gemmules'. The gemmules drop to the bottom of the pond when the dead sponge rots. These gemmules are hard and tough. They can survive cold, winter conditions. In the spring, when the water warms up, the gemmules float up from the bottom to start new sponge colonies on submerged branches and rocks.
Sponges are homes for many small animals including worms, insect larvae, and mites.
These animals live inside the sponge colony for protection. These creatures often protect their sponge home against the small animals that would eat the jelly-like sponge animals.