Cynarina Coral Care: Inflation, Light, Flow and Feeding

You open the bag and your new cynarina looks like a bare skeleton with a skin stretched over it. You float it, place it, and worry. A few days later it is twice the size, a round dome of glassy bubbles with the ribs of the skeleton showing through. That swing between flat and inflated is normal, and learning to read it is most of what keeping a cynarina is about.

Cynarina is Cynarina lacrymalis, a large-polyp stony coral that lives as a single polyp in one round cup of skeleton. It is now placed in the family Lobophylliidae, with the lobophyllias and scolymias. Reefers call it button coral, doughnut coral, cat’s eye coral or meat coral. It comes from the Indo-Pacific and the Red Sea, where it grows attached to rock on reef slopes and steep walls, often in mild current and murky water, from shallow reefs down to about 130 feet. It is listed as Near Threatened by the IUCN.

Quick facts

Scientific name	Cynarina lacrymalis
Family	Lobophylliidae (older books put it in Mussidae)
Common names	Button coral, doughnut coral, cat’s eye coral, meat coral
Form	One large polyp on a round skeleton, up to about 4 inches across. Inflated, it can look twice that.
Light	Low to medium, about 50 to 150 PAR. Our listings give 50 to 100.
Flow	Low and indirect
Placement	Bottom of the tank: sand bed or a low, flat rock, mouth facing up
Feeding	Takes meaty foods. A small meal once or twice a week.
Aggression	Sources disagree. Give it about 3 inches past its inflated edge.
Growth	Slow. It cannot be fragged.
Status in the wild	IUCN Near Threatened

Why it inflates

By day, a cynarina pumps water into its tissue and blows it up into clear bubbles. That spreads the algae living in its tissue across a bigger surface, closer to the light, and it can double the coral’s diameter. Look closely and you can see the thick septa, the stony ribs of the cup, running through the bubbles. At night it pulls the bubbles down and puts out feeding tentacles instead, and for a few hours it looks more like an anemone than a coral.

How far it inflates tells you how it is doing. A cynarina that inflates every day and shows feeding tentacles at night is in good water. One that stays shrunken for days after it has settled in is telling you something changed: light, flow, a neighbor, or the water. Size also swings for harmless reasons. It shrinks while it digests a meal, and it can look smaller one day and fuller the next. Judge it over a week, not an afternoon.

Cynarina vs scolymia vs acanthophyllia

All three are big single-polyp corals, they get mixed up in the trade, and the photos do not always make it easy. Two things set cynarina apart:

• Translucent bubbles. Inflated cynarina tissue is glassy, often clear enough to see the white septa underneath as radiating ridges. Scolymia and acanthophyllia tissue is usually more opaque.
• Big septal teeth. On the skeleton, the edges of cynarina’s septa carry large, lobed teeth. Scolymia’s are smaller.

Our acanthophyllia buying guide covers how to check a large single-polyp coral before you buy it, and how acanthophyllia differs from the other two.

Light

Cynarina wants low to medium light. Published advice runs from about 50 to 150 PAR, and a coral writer who studied wild cynarina in Indonesia says about 100 PAR is more than enough. Our listings give 50 to 100. That fits where it lives in the wild, on slopes and walls in murky water.

Too much light does not make it grow faster. It makes it inflate less, and in the worst case it bleaches. If yours stays small under strong light, move it lower or into a shaded corner before you change anything else.

Flow and placement

Low, indirect flow. A cynarina is a balloon of thin tissue, and steady current pushing on it keeps it from inflating and can tear it. You want just enough movement to carry away waste and bring food past it, and no jet pointed its way.

Most keepers, us included, put it on the sand bed. The underside is rounded and seats into soft sand, and on bare rock the tissue rests against hard edges and can wear. A low, flat rock shelf works too, as long as it is stable. In the wild it is usually attached to rock, so either is fine as long as three things are true:

• The mouth faces up. Do not wedge it sideways into rockwork.
• Nothing can fall on it, and snails and hermits do not use it as a path. A single polyp has no spare tissue to lose.
• It has room to inflate without touching a neighbor.

Spacing and aggression

This is where care sheets disagree. Some rate cynarina peaceful. Others rate it moderate or aggressive and mention sweeper tentacles that come out at night and get longer as the coral grows. Two things are not in dispute: it can swell to about twice its skeleton’s size, and it is sensitive to chemicals some soft corals release into the water.

So plan for its inflated size, not its skeleton. Leave about 3 inches between its fully inflated edge and the nearest coral, and keep it well away from leathers and other soft corals that can wear it down with chemicals.

Feeding

The algae in its tissue provide most of a cynarina’s energy, and it will survive in a lit tank without being fed. Fed corals look better, though. Our listings note that cynarinas fed directly thicken up noticeably.

• What: meaty foods. Mysis, brine shrimp, small pieces of krill or shrimp, or an LPS pellet.
• When: after the lights go out, or any time you see feeding tentacles. Turn the pumps down for 15 minutes so the food stays put.
• How much: a piece about the size of a mysis or two. Let it close over the food.
• How often: once or twice a week. More is not better, and every meal it does not eat ends up as nitrate.

After a meal it may pull in and look odd for a day while it digests. That is normal. If your fish steal its food, feed them at the other end of the tank first.

Water and growth

Our listings call for salinity 1.025 to 1.026, temperature 76 to 78°F, alkalinity 8 to 9 dKH, calcium 420 to 440 ppm and magnesium 1300 to 1400 ppm. Stable numbers matter more than perfect ones. Care sheets rate cynarina anywhere from easy to advanced. Either way, it shows a swing quickly by staying deflated.

It grows slowly, and since it is one polyp, it cannot be fragged. Slow growth and no fragging are a big part of why a well-colored piece costs what it does. Treat a cynarina as a long-term animal: put it where it will stay, and leave it there.

Common problems

What you see	Likely cause	What to do
Flat and shrunken right after arrival	Shipping	Normal. Full inflation can take several days. Leave it in one low-light, low-flow spot.
Stays small weeks later	Too much light or flow	Move it lower and out of the current before changing anything else
Shrinks for a day after feeding	Digesting	Normal. Feed less often if it never recovers between meals.
Torn or bare patch of tissue	A jet, a falling rock, a snail or hermit path, or lifting it out while inflated	Fix the cause, keep the water clean and stable, and watch the spot for spreading
Inflates less and less over weeks	Water quality slipping, or a soft coral nearby	Check your test log and nitrate, and move it away from leathers
Never shows feeding tentacles at night	Still settling, or stressed	Give it time. Check flow and light first.

For pests that ride in on corals, see our coral pest guide.

Acclimation and dipping

Corals do not need a drip. Turn the tank lights off and float the sealed bag for 15 minutes to match temperature. Open it into a clean container and add a little tank water every few minutes for 15 to 20 minutes. Dip it following the label, rinse it in clean tank water, and throw the bag water away. Set it flat on the sand bed in low light and low flow.

One rule for the life of the coral: never lift a fully inflated cynarina out of the water. The weight of the water in its tissue can tear it. Give it a gentle shake underwater so it pulls in, then lift it by the skeleton. Our acclimation and dipping guide has the details, and our coral dips are in the store.

FAQ

The Underwater Gardener is a reef aquarium store in Key West, Florida. Quarantined: held at our Key West facility for at least 4 weeks and dipped multiple times before it’s offered for sale. Livestock ships UPS Next Day Air on Tuesdays and Wednesdays.