It is important to have sea sponges in your tank as damp sea sponges are a great source of humidity in your crabarium.
Make sure they are natural sea sponges and not bleached or treated with chemicals.
Sea sponges have to be rinsed and dried. It is best to have two sea sponges so that you can alternate them in your tank.
That enables you to dry the unused sponge in the sun to further sterilise it.