Those are spawning mops there. I have those set up because they are very cheap to replace when the gars try to destroy them. Used to use plastic plants with a weighted base but they would rip off a couple stalks per day.
Tons of interesting behaviour, nothing spawning related though. Still have a couple years before any of them are sexually mature I think. Seems to be the typicalish heirarchy issues and how those change within the group. Over the last two weeks or so the two footer has now become the boss of the pond, stealing food from the big guys, nipping at the small ones, even tried to bite me earlier today. Other than that there always seems to be some sort of following of one of the bigger gars by the little ones. They seem to use the bigger gars for cover at times. The gar piles are interesting to see as well.
Within the next month, weather permitting, I'm going to be moving them to an outdoor setup. I think it will be interesting to see if the behaviour changes after that.