Sea sighting – Cassiopeia ‘the upside down jellyfish'



Images: Kade Mills

CReefs participants Jo, Kade and Lizzie were taking a recreational snorkel off the beach at the research station when they spotted a most intriguing little creature - the Cassiopeia, otherwise known as the ‘upside down jellyfish'.

The Cassiopeia lies on its bell, upside down, on the ocean floor and has tentacles that direct up in the water column. This posture enables the zooxanthellae (symbiotic algae that lives in its tentacles) to photosynthesise.
Jo Browne, one of the scientists who spotted this unusual jellyfish, will be studying it as part of her research on Lizard Island.
"I'm going to look at them to see if they have symbiotic animals living in association with them, and also study what they're eating. I'll be looking at whether they have plankton on their oral arms or in their gut cavity," Jo said.


Images: Kade Mills

She said that Cassiopeia are found in tropical waters where the water is clearer due to less plankton, so they can lie more easily in the shallow water where the sunlight is most direct.
The invertebrates' bodies are made up of 95 per cent water, three per cent salt, and two per cent protein.
"The ones we've seen out here are quite small," Jo said.
The Cassiopeia does have a sting, but is essentially harmless to humans.