A new Floor cup coral found under Edit Town / World Editor / Landmarks. Also found under Decor / Sculptures, costs 0. You need Ambitions or a later pack for the coral to show up in your game.
I'm running Paradise Island to allow scuba diving as shown in the pictures below.
Floor cup coral
Sea weed - World Editor
Kelp - World Editor
Elkhorn coral - World Editor
Pirate treasure - World Editor
Candelabrum coral - World Editor
Tiki King Polynesian statue - World Editor