Went snorkeling and came across a jellyfish with cauliflower-like appendages and rather beautiful sky-blue coloration? If you’re in Eastern Australia, you may just have met the elegant blue blubber jellyfish.
Below, find out how to identify a blue blubber jelly, where they can be found, whether their stings are dangerous, and everything else you may want to know!
| Name (common, scientific) | Blue blubber jellyfish, jelly blubber, Catostylus mosaicus |
| Family | Pelagiidae |
| Spread | Eastern Australia (mostly) |
| Habitat | Shallow waters |
Blue blubber jellyfish description
The jelly blubber (Catostylus mosaicus) is a medium-sized jellyfish whose bell can reach a diameter of up to 12″. It belongs to the order Rhizostomeae, which can be recognized by the lack of tentacles on the edges of their bell. Jellies in this order sport eight ruffled oral arms (which have a texture reminiscent of cauliflower), which they can use to transport minute food particles to their mouth.
Although we call it the “blue blubber jelly”, this species isn’t necessarily always blue in color (though it can be!). There are various color morphs, which also include an opaque off-white and a chocolate brown hue.
Based on the different colors, a 2005 study categorized Catostylus mosaicus into two different subspecies: C. mosaicus mosaicus and C. mosaicus conservitus. The former is usually brown and is generally larger, while the latter can range from white to blue and may have small body spots called papillae.
Blue blubber jellyfish habitat
Blue blubber jellies are mostly naturally found in Eastern Australia (Queensland, New South Wales, Victoria) and Tasmania, where huge blooms can completely overwhelm the coastline. Catostylus mosaicus mosaicus, the brown color morph, is noted to be more common in Victoria and Tasmania, while C. mosaicus conservitus, the blue color morph, is more frequently spotted in New South Wales.
All this being seen, as can be seen on iNaturalist (one of my absolute favorite tools to identify wildlife), blue blubber jellies been seen in places as varied as the Malay Peninsula, Sri Lanka, and South Africa.
In their natural habitat, jelly blubbers mostly stay in the shallows. They’re primarily found in estuarine environments (especially the parts with higher salinity levels), bays, and lagoons. They have a particular appreciation for clear water.
Blue blubber jellyfish diet
Jelly blubbers feed mostly on tiny zooplankton. Their favorite foods include plenty of larvae, like those of copepods (nauplii), molluscs, and similar. The prey is captured in the ruffled oral arms, which transport the food to the jelly’s mouth at the center of the bell.
A 2005 study shows that blue blubber jellies are particularly efficient at catching mollusc and bivalve larvae. Another paper, published in 2008, concludes that’s about the extent of their talents: they mostly fail to catch crab, shrimp, and fish larvae.
Did you know? As always with jellyfish, it’s eat or be eaten. Jelly blubbers are on the menu for turtles, as well as jellyfish-eating fish like tuna. Oh, and for humans, too—marinated blue blubber jellyfish salad with sesame is pretty common in some parts of China.
Planning your next snorkel trip?
Blue blubber jellyfish facts
Jelly blubber sting
If you accidentally stepped on or brushed past one and are now experiencing skin irritation, you may be wondering: do blue blubber jellyfish sting? And if so, should I be worried? The answers to these questions are yes, and no.
All jellyfish possess nematocysts, also known as stinging cells, which contain tiny harpoon-like structures that can “shoot” poison into their prey—or unsuspecting humans. Luckily, in the case of the blue blubber jellyfish, these nematocysts don’t contain very potent toxins.
Scientists have found that blue blubber jellies boast four different nematocysts, and they have them in relatively large amounts. Despite this, the species’ sting is mild (though it can be pretty irritating) and not severe to humans.
As such, this jellyfish is by no means on the list of most dangerous jellies. To relieve any irritation, which can be reminiscent of the annoying sensation of a stinging nettle, you can follow normal jellyfish sting protocol*:
- Rinse abundantly with saltwater.
- Soak in water that’s as hot as you can handle (105-115 °F or 40-45 °C works well).
- If you still see tentacle bits, remove them using tweezers or the edge of a credit card. You can also try carefully shaving the area with a sharp razor to scrape them off.
*Vinegar is often used for jellyfish stings, but recent research suggest it only really works with box jellies; for many other species, it makes the sting worse. I recommend sticking to universally safe relief options like those discussed above. Seek medical advice if you think you’re having a severe allergic reaction (anaphylaxis).
Reproduction & life cycle
Jellyfish are pretty weird creatures, and the way they reproduce and grow is no exception. Jelly blubber males and females are identical in looks and occur in an exact 1:1 ratio. According to research, they spawn throughout the year, except in winter.
The jellies carry the larvae (planulae) until they’re ready to go out into the world by themselves. Once they do, the planulae have quite a journey ahead:
- First, they use their propulsion hairs (cilia) to move them to a suitable place to settle, such as wood or rock.
- Upon settlement, the planulae transform into polyps. These start out with four tentacles, but grow more as they eat and develop.
- Once they have a good number (up to 20) of tentacles, the polyps will start to reproduce asexually. They grow new polyps on themselves, which then break off (budding).
- Eventually, after as little as 15 days, the polyps begin to produce segments and release them. Each of these, called ephyrae, can form a new baby jelly. Ephyrae are free-swimming and will slowly grow into mature jellyfish (the medusa stage).
Jelly & friends
There are many highly specialized creatures in the world, some of which are associated with jellyfish. Indeed, all jellies have their own specific parasites, and they can also maintain symbiotic (mutually beneficial) or commensal (beneficial for one, but not harmful for the other) relationships with completely different species.
Researchers have identified at least three jellyfish “friends”:
- The isopod Cymodoce gaimardii (likely commensal): live on the jelly, likely feeding on it and using it for shelter.
- The anemone Anemonactis clavus (parasitic): lives on the jelly, potentially using it as a nursery and dining hall until it matures and moves to the seafloor.
- The copepod Paramacrochiron maximum (likely commensal): lives almost exclusively on the jelly, feeding on its mucus.
If you have any more questions about the blue blubber jellyfish or if you’d like to share where you spotted this jelly, be sure to leave a comment below!
Sources & further reading
Browne, J. G., & Kingsford, M. J. (2005). A commensal relationship between the scyphozoan medusae Catostylus mosaicus and the copepod Paramacrochiron maximum. Marine Biology, 146, 1157-1168.
Browne, J. G., Pitt, K. A., & Norman, M. D. (2017). Temporal patterns of association between the jellyfish Catostylus mosaicus and a sphaeromatid isopod and parasitic anemone. Marine and Freshwater Research, 68(9), 1771-1777.
Carr, E. F., & Pitt, K. A. (2008). Behavioural responses of zooplankton to the presence of predatory jellyfish. Journal of Experimental Marine Biology and Ecology, 354(1), 101-110.
Dawson, M. N. (2005). Morphologic and molecular redescription of Catostylus mosaicus conservativus (Scyphozoa: Rhizostomeae: Catostylidae) from south-east Australia. Journal of the Marine Biological Association of the United Kingdom, 85(3), 723-731.
Loveridge, A., Pitt, K. A., Lucas, C. H., & Warnken, J. (2021). Extreme changes in salinity drive population dynamics of Catostylus mosaicus medusae in a modified estuary. Marine Environmental Research, 168, 105306.
Peach, M. B., & Pitt, K. A. (2005). Morphology of the nematocysts of the medusae of two scyphozoans, Catostylus mosaicus and Phyllorhiza punctata (Rhizostomeae): implications for capture of prey. Invertebrate biology, 124(2), 98-108.
Pitt, K. A. (2000). Life history and settlement preferences of the edible jellyfish Catostylus mosaicus (Scyphozoa: Rhizostomeae). Marine Biology, 136, 269-279.
Pitt, K. A., & Kingsford, M. J. (2000). Reproductive biology of the edible jellyfish Catostylus mosaicus (Rhizostomeae). Marine Biology, 137, 791-799.
Pitt, K. A., Koop, K., & Rissik, D. (2005). Contrasting contributions to inorganic nutrient recycling by the co-occurring jellyfishes, Catostylus mosaicus and Phyllorhiza punctata (Scyphozoa, Rhizostomeae). Journal of Experimental Marine Biology and Ecology, 315(1), 71-86.
Wiltshire, C. J., Sutherland, S. K., Fenner, P. J., & Young, A. R. (2000). Optimization and preliminary characterization of venom isolated from 3 medically important jellyfish: the box (Chironex fleckeri), Irukandji (Carukia barnesi), and blubber (Catostylus mosaicus) jellyfish. Wilderness & Environmental Medicine, 11(4), 241-250.