When you see a coral reef from a distance you can make out individual coral structures however there often seems to be a blanket of coral between them. The blue soft coral you can see in the illustration gives an idea of this blanket effect
The challenge is how to achieve that general appearance re-using something around the house.
Things from home, second hand or at the recycling depot can really add to your composition.Here is a big fluffy knitted shawl. It can be used on its own or you can take another strip of a different coloured fabric and poke it up through the holes in order to indicate coral polyps.
Another suggestion would be to use an old afghan (knitted or crocheted blanket) or even a 'remnant' or leftover piece of fabric to create a base for your other coral colonies to rest upon.
The right material of a complimentary colour to your other corals will be just the thing you need to get that special effect you are looking for.