What reef tank inhabitant can do a 15 minute spawn?

[jimsar]

I was treated to a 15+ minute "roman candle" show just before midnight, New Year's eve. There's been contrary opinion, but I still believe a sponge is responsible. Here's a pic:

What do you folks think? Can a sponge, fist sized at best, expel this much sperm? A more detailed description of the event is actually posted on this thread:
http://reefcentral.com/forums/showthread.php?s=&threadid=741099