Ewwwe, looks like both mesenterial filaments and gametogenic tissue, but it doesn't seem to be suffering.
However if a fish, crab, worm or anything else decides that just might be a tasty meal then....well.... just keep an eye on it.
I'm afraid it will have to try to heal itself, wish there were something like a liquid bandaid made for anemones.
Hmmm. I wonder if you could protect it by cutting a piece of PVC pipe and placing the column in it? you know partly burried in the sand? Just an idea if things become and emergancy and something is trying to eat it where the wound is. Just a thought.
Not that the darn thing would stay there, no doubt it would try to move right away.
One other thought, check it out with a flashlight at night and see if anything is crawling around the wound.
Good luck.
Thomas