I would say high light for the coral, and moderate flow for the worm. Occasion phytoplankton as reefnutz says, and ditto the part about predators like arrow crabs.
Some shrimp may be blamed for the death of an already dismised worm when they go after the dead body, since I have never see shrimp that can kill a healthy worm. Nothing more seriously that causing the worm to withdrawn into the hole for a few minutes, but arrow crab may not be as harmless.
From the appearance of the worm and coral, it is in very good health. Make sure the coral does not get darken, since it is a indication of insufficient light level. All in all, it is a very slow grower. I have one that is more than 5 yrs old, and it is about the same size.