Related Articles: Jellyfishes, Scyphozoans, Hydrozoan Jellies, Hydrozoans, Cnidarians, FAQs by Group: Cassiopeia/Upside Down Jellies,
Cassiopeia for Jellyfish Tanks Bob Fenner

The use of Cassiopea for “Jelly Aquariums” is definitely underappreciated. Though some of the several providers of Scyphozoans for ornamental purposes do offer the genus, and they are still darlings of the public aquarium experience; they’re underrepresented as worthwhile species in specialized circulation systems.

            Cassiopea, Mangrove or so-called Upside-Down Jellyfish, should be preferred on a few counts. They’re beautiful, hardy, ship well, are easily fed, and are VERY common in shallows in many places of the world’s shallow tropical seas; being very easy to collect. This isn’t all; they have a few other “better than other choices” characteristics for home hobbyist use as you’ll soon appreciate.

 

Abundance & Distribution:

            The only member genus of its family Cassiopeidae, there are eight recognized species of Cassiopea. They’re found, often in goodly numbers in shallow, calmer near-shore habitats like mud flats, seagrass beds, mangroves and canals; occurring in browns, tans, greens, white, blue and mixed colors, some with a good deal of transparency to their bodies. To heck with boring, colorless Moon/Aurelia jellies!

Some Cassiopea from around the world to give an idea of their diversity. At right, C. frondosa in Jamaica (Usually amber to olive green in color); have been to places in the Florida Keys where they were so numerous it was hard to not step on them.   Below a largely transparent Cassiopea in N.E. Sulawesi, and one in the Gulf of Aqaba, Red Sea.

 

            Cassiopeids belong to the Order Rhizostomeae; meaning “root mouths”; in reference to the look of their food gathering and processing arrangement. Cassiopea lack the tentacles and central mouths of most Jellyfishes. These animals instead have eight branched arms radiating from the center of their circular bells; these arms bear numerous funnel-shaped openings that function as suctioning mouths. The coalescing of paths from the mouths to the stomach gives the appearance of an inverted tree; hence the “root mouth” naming.

            And yes; they do live upside down, near or on the bottom; pulsing gently to move water about for oxygen, dispersing wastes and bringing small planktonic food close for filter-feeding consumption.

            Some specimens have been measured at more than ten inches in the wild; but most are 3-5 inches in diameter, and very slow growing.

 

Compatibility:

            Though they don’t have potent stinging potential, Cassiopea do release Nematocyst “grenades” into the adjacent water when disturbed. Hence, it is best to leave fishes out of their system, and stock only with algae, plants like Mangroves, and hardy invertebrates that won’t puncture the jellies.

 

Systems:

            Tanks: Can be of modest size; 30-40 gallons for a specimen or three if small; better flat and wide rather than tall and narrow in aspect, as again, Cassiopeia spend their lives on the bottom.

            Circulation: The members of this genus can be easily kept in a “non-Kreisel” type recirculating system, as they propel themselves and almost always are near or on the bottom. What one needs to arrange is either a laminar or gyre flow that is not too brisk to sweep them up on onto overflows or pump intakes, but sufficiently complete and vigorous to provide good water movement.

            Lighting: Unlike many of the more popular aquarium jellies, Cassiopea enjoys and benefits from “reef system” lighting. These animals live mostly in waters of a few to several foot depths, oriented as they are to utilize sunlight in food-producing photosynthesis. It is best to have your lighting on timers for regularity, and provide strong (as in direct sun overhead) lighting several hours per day.

            Temperature et al.: These are tropical animals, so temperatures in the low seventies to low eighties F. suit them fine. Otherwise, “reef” conditions of specific gravity (1.025-6); pH (8.2-8.4), biomineral and alkalinity, and a dearth of accumulated metabolite are called for.

A nice Cassiopea on exhibit at the Camden, New Jersey “Adventure Aquarium”. Some public and private collections utilize Kreisel and other circular rotating technology for keeping upside-down jellies, but this is not necessary for these largely bottom dwelling animals

 

Nutrients Needed:  Notice that these animals live in shallow areas of highly fluctuating physical qualities; but that they do need some measurable N, P, K (Nitrate, Phosphate and Potassium) to sustain them chemically for food.

 

Foods/Feeding:

            In the wild, Cassiopea feed on particulates and small plankton. They can be sustained in captivity with introduction of blended mashes of seafood items and small crustaceans, or a commercial zooplankton product. A feeding a day is fine for most settings, with care given to take care (rinsing or change out of mechanical filter media) of removal of uneaten materials after feeding. Mowka (1974) mentions the periodic use of commercial food tablets, dissolved and dropped onto the arms as being adequate.

            Monitoring to see if your Mangrove jellies are getting enough food is easy. Cassiopea will shrink in size and weight if overly starved, losing up to 4/5’s of their bodies.

 

Disease/Health:

            Mangrove jellies are environmentally tough, tolerating vacillations in temperature and salinity like few other invertebrate animals.

 

Dangers in Human Handling:

            Cassiopea species are mostly photosynthetic and don’t have a very potent sting; in fact, it’s barely noticeable. However, as with most such toxins, some folks are more sensitive to others in getting stung. The best measure to take in avoidance is to keep your hands and arms out of their system period. IF you need to get into the tank, use long-handled tools and/or very long gloves to prevent all water/skin exposure.

 

Reproduction:

            Cassiopea medusae are dioecious (Greek for “two houses”, separate male and female as individuals). Females retain their eggs in small openings in their bodies on their oral disks called reproductive vesicles which are fertilized by nearby males. The fertilized ova are retained until they’ve developed into planula larvae. These in turn are released to find suitable substrate, metamorphosing in turn to sedentary polyp and tentacled scyphistomae; that subsequently mature to split off (strobilation, like other jellies) free-swimming medusae/jellies.

 

Cloze:

            Decades back I was in the marine livestock collecting business and since then have had many occasions to ask other collectors why they don’t gather and sell Cassiopea. For most it’s been a “Meh; too easy to do so”, and/or “Who would pay for them?”

            If you’re going the Jelly route, I entreat you to consider the genus. They’re really neat animals and especially compared with the many other species available… are far more suitable for aquarium use; being tropical, not too sticky (easily torn), being and staying small.

Keep your eyes open when out diving where these animals are! Here’s one serving as camouflage and more for an Ethusa sp. Crab in N. Bali, Indonesia.

 

 

Bibliography/Further Reading:

https://en.wikipedia.org/wiki/Cassiopea

Mowka, Edmund J. Cassiopea. Marine Aquarist 5(3), pp 48, 49.