Breaking coral and coral fans with silk touch pickaxe does not decrease durability, which means endless mining of coral and coral fans without breaking the pickaxe.
Recreate:
Enchant diomand pickaxe with silk touch
find coral reef
mine some coral or coral fans
durability will be the same as you would not break anything
this is true, BUT so it is for breaking dead shrubs and grass, although they will drop sticks and nothing respectively.
The pickaxe will not lose durability. True.