We can find plenty of coconut husks every time.
And those will provide ample space for plants.
We prefer coco husks.
We use shells for decoration ,spoons , containers and ornaments.
some times as salt containers bec no acids there.
I suppose with contact of water and due the high rain fall through out the year (approximately 70" ) shells are pruned to decay soon.
We do not need shells bec there are plenty of tree trunks here so we can tie them up .