By Bob Goemans
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Plerogyra sinuosa

(Dana, 1846)

Bubble Coral, Bladder Coral, Grape Coral, Octobubble Coral, Pearl Coral

Likely Reef Tank Suitable

Range: Red Sea, Indo-Pacific Ocean, Australia, Indian Ocean, and Eastern Africa

Natural Environment: Usually found in protected shaded areas, often containing high nutrient levels/quite murky/turbid that receives gentle water movement. In these areas, e.g., lower reef slopes, under overhangs and cave walls, they are often found in a vertical position. Specimens over 3 feet (1 m) across have been seen in the wild.

General Husbandry: Besides light and water quality issues, understanding the construction of the skeleton and polyp is part of the key to successfully maintaining this species. - Its skeleton develops a somewhat flattened, yet continuous and unbranched wall of fused vertical plates (septa). They are easily broken during collection and shipping, and something to check on before purchase, as broken plates often lead to the demise of this species. As to the surface areas of its water filled bubble-shaped polyps (vesicles), they contain zooxanthellae and expand during the day and mostly retract at night. Bubbles are usually .5 to 1.0 inch (1 - 2.5 cm) in length, sometimes larger. Bubbles retract somewhat at night and the coral displays long sweeper tentacles, sometimes 3 or 4 inches (7.5 - 10 cm) in length or longer that can sting downstream neighbors within reach. They are also capable of stinging human flesh, so be forewarned. It should be noted the short tentacles associated with the bubbles during the day do not contain stinging cells, yet the sweepers extended during the night do contain stinging nematocysts. Tapered feeding tentacles emerge at night to capture plankton.

It is thought bubble size regulates the amount of light its zooxanthellae receive, since this coral does not photoadapt, i.e., adjusts its level of photosynthetic cells to match light intensity. It simply regulates how much light they see with bubble size. Therefore proper placement is extremely important, as most prefer low light and do better with indirect light and gentle water movement. Yet, some specimens seem to do well in direct light provided by fluorescent lamps, but would not recommend strong direct light from metal halide lamps.

This photosynthetic stony coral is also a suspension feeder and accepts zooplankton when its feeding tentacles are displayed. Therefore, its possible to directly dose the polyps with meaty foodstuffs, e.g., fortified brine shrimp, mysis, rotifers, and/or products containing Cyclop-eeze. As a note of caution, I have found overfeeding to cause the specimen to go through odd shape changes that seem to affect its longevity. Therefore feed sparingly, e.g., twice monthly. Keep in mind if the water movement is too swift, the bubbles will not fully expand, detracting from the natural nourishment provided by the zooxanthellae on the surface of each bubble.

Overall, this is generally a hardy coral and the following water parameters should be heeded: Calcium 380 - 430 ppm, Alkalinity 3.5 meq/l, Mg - approx. 1300 ppm (relate to actual specific gravity), pH 8.1 - 8.2, Specific Gravity 1.025, Phosphate < 0.015 ppm, and a temperature range of 74 to 83°F (23 - 28°C).

 Plerogyra sinuosa (Bubble Coral, Bladder Coral, Grape Coral, Octobubble Coral, Pearl Coral)
Photo © Bob Goemans
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Ocean Nutrition