I believe I discussed plate corals a few months ago in the context of how I made them for my small fiber art projects. I have recently been figuring out how to make them for display in our reef.
This is a fingering weight yarn that I have been crocheting held double so a single strand of sport or Aran weight yarn would probably give you a similar feel. I simply single crochet a circle until I get it large enough to make me happy and then I alternate using single crochet for some sections and double crochet for other sections which gives it a wavy edge.
I am then sewing it onto plastic canvas to make it flat and sturdy and crocheting a tube for it to stand on. I then sew the tube onto the plastic canvas. The tubes will then be stuffed and once I complete five or more, I will put them all together and sew them onto a base. I want to keep their edges overlapping so the tube height has to be variable.
I know that it can be cringe worthy to use plastic canvas but I always source my plastic canvas from resale shops. Recycling it is the best way to go.