what goes on after lights out...

[fishface]

was wondering if anyone can tell me what, and where all the little extenders are coming from outta my live rock when the lights go out. they're sweeping around and seemingly comin' outta no where...are they harming my corals? the sweepers seem to come in contact with some xenias, is this making them close up? these goulies only seem to come out after dark ...any ideas folks??

darryl