«shuffling» — changes in the relative abundance of zooxanthellae clades that are already present in the coral tissue (reefresilience.org)
Coral and algae called zooxanthellae live in a mutual help relationship. (climatechangenews.com)
Yes, they are bivalves, but species in the genus Tridacna might as well be treated as hard corals since their mantles contain symbiotic zooxanthellae algae similar to that in corals. (petbusiness.com)