They close up every once in a while. It's totally normal, though I've never had one spawn. It looks like yours is the blue/green type. They don't seem to drop tons of branches the same way the normal brown capnellas do. The best thing you can do is leave the coral alone. Chances are very slim that you'll have any eggs that survive into new corals. Besides, the eggs that get released will most likely either be fish food or get filtered out by your skimmer or other filtration. I say watch it and enjoy it. Not everyone gets to see corals spawning in their tanks. I've seen it once in 7 years with a large toadstool.
