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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!
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.
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.
Bibliography/Further Reading:
https://en.wikipedia.org/wiki/Cassiopea
Mowka, Edmund J. Cassiopea. Marine Aquarist 5(3), pp 48, 49.
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