Bubble coral care

Quick reference

What is a bubble coral?

Plerogyra sinuosa ranges across the Red Sea, Indian Ocean and West Pacific; P. simplex is West Pacific only, and Physogyra lichtensteini, the smaller-bubbled "pearl bubble", is as widespread as P. sinuosa.^[1] TFH says it lives in shaded, protected places on lower reef slopes, cave walls and under overhangs, usually growing vertically.^[2] The bubbles are modified, water-filled tentacles, usually 0.5–1 inch across and up to about 2 inches when fully inflated, that swell in daylight to expose their symbiotic algae to more light.^[1]

Lighting for a bubble coral

Sources differ. TFH's species profile recommends low, indirect light and warns against strong direct metal halide light, noting that the coral seems to control light by changing bubble size rather than its algae, so placement matters.^[2] A second TFH article says it lives in both turbid and brightly lit water and adapts to a wide range, its author keeping one two-thirds of the way up the rock under compact fluorescents for years.^[3] Tan and brown specimens tolerate less light than pale green or pink ones.^[2] Both agree on acclimation: wild colonies from dim water can suffer light shock, so start low and move it up over at least a couple of weeks.^{[1, 3]}

Flow and placement

Moderate and indirect: enough to make the bubbles sway and stay clean, but TFH warns not to blast it with a powerhead, and strong flow stops the bubbles expanding fully, which cuts what the coral gets from its algae.^[2] Reefs.com recommends low to moderate turbulent flow that moves the tentacles without preventing full expansion, and notes sweeper tentacles are produced most often in fast flow.^[1]

Feeding

It's photosynthetic but also catches zooplankton with feeding tentacles that extend a couple of inches.^{[2, 1]} Reefs.com says it takes brine shrimp and chopped fish, clam or shrimp and can be hand-fed; one TFH writer fed mysis or brine shrimp weekly and saw it grow and multiply,^[3] while TFH's species profile feeds small foods sparingly, about twice a month, after overfeeding and large chunks caused odd changes in shape.^[2] Either way, don't overfeed.^{[1, 3]}

Aggression and spacing

At night the bubbles shrink and sweeper tentacles of 3–4 inches (7.5–10 cm) come out, three or four times the length of the feeding tentacles, and sting neighbours within reach, especially downstream.^{[2, 1]} TFH recommends 5 or 6 inches between it and other corals, a little less on its up-current side; a neighbour that stops opening, or tissue damage on the side facing the bubble, means one of them should move.^[3] Reefs.com found colonies of the same species tolerated each other.^[1]

Tankmates

Give it more room than its daytime size suggests, and keep corals you value out of its downstream side.^{[2, 3]}

Disease and quarantine

The skeleton's large, sharp septa make it easy to injure in collection, shipping and handling, and broken septa cut the flesh.^{[1, 2]} Reefs.com says injuries are often followed by brown jelly infection, typically fatal and able to consume flesh within hours to days.^[1] Never lift one out of the water with the bubbles inflated: their weight can tear the tissue, so shake it gently and let them deflate first.^[2] Recession exposing skeleton is usually linked to low alkalinity or calcium or high phosphate.^[1]

Fragging and propagation

In aquaria it reproduces asexually: buds form on the lower edge of the flesh and can drop off, attach and grow, and tissue that spreads over the skeleton onto the rock can form a new colony.^[1] Captive spawning hadn't been reported when Reefs.com published.^[1] One TFH writer saw his colony multiply with weekly feeding.^[3]

Safety

Troubleshooting

Common mistakes

• •Lifting it out of the water with the bubbles inflated.^[2]
• •Placing it under strong direct light.^[2]
• •Strong flow that keeps the bubbles closed.^{[2, 1]}
• •Too little space for the night-time sweepers.^{[2, 1]}
• •Overfeeding large chunks.^[2]

Equipment & food for this species

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Most LPS benefit from occasional target-feeding, and a dip on new frags catches hitchhiking pests before they reach the display.

Bubble coral FAQ

How much light does a bubble coral need?

Low to moderate and indirect is the safe start; TFH sources differ on how much more it tolerates, and we found no published PAR range.^{[2, 3]}

Is a bubble coral aggressive?

Yes at night: sweeper tentacles of 3–4 inches sting neighbours within reach.^{[2, 1]}

Why won't my bubble coral open?

Flow that's too strong, unsuitable light, or injury. TFH says strong flow stops the bubbles inflating.^{[2, 1]}

Do bubble corals need to be fed?

They benefit from small meaty foods, but TFH fed only about twice a month after overfeeding caused problems.^{[2, 1]}

Can you frag a bubble coral?

We found no reliable fragging method; in aquaria it reproduces by buds that drop off and settle.^[1]

Can bubble coral sting people?

TFH says the sweeper tentacles can sting human skin.^[2]