Upside-Down “Upside Down Jellyfish”

During mangrove tours where you get out of the kayak, some wiseguy always reaches down and scoops one up to show it off. So here at the surface is an upside down jellyfish …upside down.

TWO DENIZENS OF NOTE IN THE MANGROVE ENVIRONMENT are Cassiopea fronosa and Cassiopea xmanchana, both better known by the common name “Upside Down Jellyfish” (as we pseudo marine naturalist know, they should be called sea jellies but all the sources I.D. them as jellyfishes).

Righting itself, it drifts downward…
…to resume its natural position.






NORMALLY ON THE BOTTOM   Although they can swim, upside down jellies spend most of their time lying on their backs in shallow waters – mostly mangrove inlets – catching rays. Literally. They do use their tentacles – which offer only a mild sting – to catch plankton and other small invertebrates that pass by.

ZOOX-ENDORSED   But they are blessed with the presence of zooxanthellae – the dinoflagellates that power-feed corals – in their tissues, and pass the time extending their short tentacles upward to facilitate the zooxanthellae’s photosynthetic services.

The zoox provide them with both nutrition and their coloration. The colors can vary depending on the zooxanthellae. This one, with brown bands, most resembles the C. xmanchana in Paul Humann’s Reef Creature Identification – Florida, Caribbean Bahamas, although its bands are blue-green. But both species are distributed worldwide. Although mild, their stings can cause redness and welting.

PRINCIPAL SOURCES: Encyclopedia of Life, “Upside-Down Jellyfish,”; Florida Keys National Marine Sanctuary, “What are the most common jellies in the Keys?”; Reef Creature Identification, Florida, Caribbean, Bahamas, Paul Humann, Ned DeLoach

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