[Gary Majchrzak]

all anemone spawnings in my aquarium (S.haddoni, M. doreensis, S.gigantea) have occurred late in the afternoon photoperiod.
A 'puckering up' of the anemone is usually observed before the actual spawning event. Fishes usually eat gametes.
I don't think any of my anemones had 'stress spawns'.
If I had to pin it down to any one condition that might have triggered the spawns it would be the sun. Late afternoon sunlight shining on each anemone in early spring and early autumn.