Bubble Coral

During the day the bubble coral covers the top of its skeleton with grape-sized, water-filled, semi-translucent bubbles. The bubbles deflate when touched or when the flow gets strong. In the evening, when the lights go out, the bubbles shrink and hunting tentacles open between them. The skeleton under the bubbles consists of thin, sharp-edged septa; this is why the skeleton easily causes wounds when the tissue tears.

The color is mostly cream, light green or bluish gray. Plerogyra, placed in different families over the years, is now in the family Plerogyridae. Its trade is subject to CITES Appendix II; besides wild-collected colonies, aquacultured frags are also available, so choose those.

• Green bubble: Light green bubbles with a fluorescent tint.
• White or cream bubble: The most common, natural color form.

It lives in sheltered reef environments in the Indo-Pacific, often in turbid water, in rock crevices and under shaded ledges. It is not very common in the wild. Being used to calm, dim surroundings explains why it wants low flow and moderate light in the aquarium.

• Light: Low to moderate, about 50–150 PAR. In strong light the bubbles stay small.
• Flow: Low and indirect. The bubbles should sway gently; if placed near a pump outlet they tear.
• Placement: The lower zone of the rockwork or a rock on the sand. When the bubbles inflate, the colony can double in size; plan its placement according to its inflated size.
• Water parameters: Salinity 1.024–1.026, KH 7–10 dKH, calcium 400–450 mg/L, magnesium 1250–1350 mg/L. It is tolerant; the bubbles may deflate after sudden salinity changes. Nitrate 2–10 mg/L and phosphate 0.03–0.1 mg/L are suitable.

It is photosynthetic; the bubbles help it gather light better during the day. It makes good use of supplemental feeding: once or twice a week, in the evening when the tentacles open, give mysis, chopped shrimp or LPS food. Instead of leaving food between the bubbles during the day, wait for the tentacles to open.

It is an aggressive coral. At night, in addition to its normal tentacles, it puts out stinging "sweeper" tentacles that can reach 10–15 cm. Leave at least 15 cm of space between it and neighboring corals. The bubbles that inflate during the day can also shade the coral next to it.

Hermit crabs, some angelfish and large shrimp can damage the bubbles. Clownfish sometimes host in this coral.

The colony can be propagated by cutting between the valleys of the skeleton with a diamond-blade saw while the bubbles are deflated (after the lights go out). Because the tissue tears easily, the cut must be made carefully and the pieces watched for a few weeks under low flow. Growth is slow.

• Torn bubbles: Caused by strong flow, proximity to a pump or contact with hermit crabs; the torn spot becomes vulnerable to brown jelly.
• Brown jelly: Can spread quickly; the affected part is removed and given a coral dip.
• Bubbles not inflating: Too much light, strong flow or fluctuating water parameters.