Gigantea is not known to reproduce asexually.
It is reported to do so in the wild:
Incorporating fine-scale seascape composition in an assessment of habitat quality for the giant sea anemone Stichodactyla gigantea in a coral reef shore zone
http://www.springerlink.com/content/...3/fulltext.pdf
from it:
"At the end of the study, 43 anemones existed: nine had disappeared, six had been newly found, and one actinia had divided into three small individuals."