This is a cool thread.
I have always liked mags, so I have been looking into trying to keep a few in my tank, and maybe trying to get them to reproduce. I have a couple thoughts (I am aware H. malu are not mags, but same genus, so maybe some similarities):
The first thought was when I initially put my mag in the tank it looked like it released sperm for a little while. So possibly stress induced, or touching the air, or just long exposure to dark, like that of a storm.
The other thought I had was after reading an article about H. magnifica:
http://animaldiversity.org/accounts/Heteractis_magnifica/
I thought it was interesting that the closer towards the surface the anemones are, the more likely they are to be found singly. While colonies are likely to be found at great depths. Colonies to me implies more likely to reproduce sexually simply due to availability of partners. To me greater depths also imply less light by both moon and sun, possibly less likely for the moon and starlight to affect reproduction. The article goes on to say, “Leeward of prevailing swell of water tend to be denser populations than more exposed marine locations.” Which implies to me a protected environment lets them stay together without being thrown apart, with possible circular movement from around the rocks. Then one of the big factors to induce change might be something like a big storms (extra darkness with very oxygenated water/temp changes/short-term salinity reduction in waves).
Who knows, there is a lot of guessing in here, but I figured I would throw out a few ideas that might simulate a natural environment.
