Unlike the classic tentacled jellyfish that Dory painfully dodges her way through in Finding Nemo, the upside-down jellyfish Cassiopeia xamachana, so-called because of the way they hang upside-down on coastal seabeds, has a very different approach to prey capture. Armed with a mucus fringed with tiny explosive barbs known as nematocysts, the jellyfish releases its stinging cell structures, referred to scientifically as cassiosomes, into the water column.
As cool as this may sound, there are many questions surrounding the evolutionary drivers of such a strange adaptation. Why would jellies release their killing mechanism so the prey is caught out of reach of the adult animal?
Lead author of the research, Dr Cheryl Ames, suggests that the mucus may be used by jellyfish to draw in planktonic prey after they are stunned and killed. With the potential to limit damage to the tentacles which are more energetically expensive to regenerate, the mucus could be the answer to targeting prey in large quantities. It may even be possible that the mucus could act as a floating food source trapping the prey within, with the stinging nature of the mucus acting to deter other predators, reserving the prey for Cassiopeia.
With no shortage of his own ideas, one of Newcastle’s very own marine scientists, Dr Gary Caldwell, is excited by the recent developments. He suggests that the chance of one jelly recapturing prey from the mucus it released itself is very small - so why do it?
The answer may lie with kin selection, where such altruistic behaviour favours relatives where many are present in an area. This may benefit the population as a whole by extending their scope to capture prey, with the sticky mucus carpet acting like a huge underwater spider web.
While the recent study mainly focuses on prey capture, this may not be the only role for the intriguing sticky mucus. Largely neglected in the recent research is the potential for zooxanthellae exchange. Zooxanthellae are the symbiotic algae housed within Cassiopeia’s mucus jelly, with exchange between individuals enhancing the jellyfish’s ability to derive energy via photosynthesis in shallow coastal waters.
It is possible that the stinging cells released with mucus may also act as a defence mechanism, similar to the ink ejected by cephalopods when they feel threatened.
While the jelly is often lethal to its prey, effects on human swimmers are considered much less severe. Other than a tingling sensation and irritating rash, the risk of serious injury or death following a single sting is unreported - at least not for this jellyfish.
With many more questions to be answered, research in this area is far from complete. With a brand new narrative to enhance our understanding of jellyfish, who knows where the next chapter will lead?