I tried to make a coral but was unable to fill the caps. As you can see, the option is not clickable. I also can't see options like 'Round', 'Object', or 'Profile' and I don't understand why.
I made this shape by making a UV sphere, extruding hair, and converting it to a curve, then making the spline type Bezier and Automatic handle type. Then I added depth in Geometry > Bezel but I am unable to fill in the caps.