This rather large, soft, ruffled algae became common on some southern lagoon reefs after about 2009. We have no photos nor do we remember it before then, even though it can form loose clumps up to a meter wide and is hard to miss. It may have been accidentally introduced to Kwajalein, possibly coming in attached to barges or ship hulls.
The two photos below could be something different.
Created 3 October 2020