Mangrove Upside Down jellyfish

up Little Creek on South Andros in sandy bottom bonefish flats, colonies in several places; I thought they were plants until I saw one float by; large and small; large ones on flat bottom, some small ones in little divots in the bottom; other mangrove critters like mangrove snapper, blue crabs, checkered puffers; most were dark grey, some dark orange or brown, saw one blue one