Author: Bob Goemans
Common Names: Bubble coral, bladder coral, grape coral, octobubble coral, pearl coral
Phylum: Cnidaria (stony corals)
Range: Indo and Western Pacific Ocean, including the Red Sea
Water Requirements: Calcium 380 to 430 ppm, alkalinity 3.5 meq/l, Mg approximately 1272 ppm (relate to actual specific gravity), pH 8.1 to 8.2, specific gravity 1.025, phosphate , 0.05 ppm, and a temperature range of 74 to 83 degrees Fahrenheit (23 to 28 degrees Celsius).
Natural Environment: Inhabits protected shaded areas receiving gentle water movement on lower reef slopes, cave walls, and under overhangs, and typically found in a vertical position. When found in moderately lit areas, the waters are somewhat turbid.
At night, the bubbles retract somewhat and the coral displays long sweeper tentacles, sometimes 3 or 4 inches (7.5 to 10 cm) in length, which 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.
The most common color is tan, yet some specimens exhibit a pale green or pink tinge. Some light tan to almost white colored specimens probably received slightly more light than darker brown specimens. Those with colored tints requrie slightly better lighting than brown or tan specimens. Some bubbles appear to have a fingerprint pattern on their surface.
It is thought that the size of the bubbles regulate the amount of lights its zooxanthellae receive, since this coral does not photoadapt (adjust 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. Generally, 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 I would not recommend strong direct light from metal halide lamps.
Even though it's a photosynthetic stony coral, it's also a suspension feeder and accepts zooplankton when its feeding tentacles are displayed. When I feed my aquarium, if feeding tentacles are displayed, I directly dose the polyps with meaty foodstuffs, e.g., fortified brine shrimp, Mysis, rotifers, and/or copepod-baed products. Nevertheless, I have often found overfeeding or feeding with large pieces of marine flesh causes the specimen to go through odd shape changes that seem to affect its longevity. Therefore, if the decision is made to feed, do so 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. This is generally a hardy coral and very common in the trade.
Since the animal's septa, i.e., the upright large blade-like structures that extend above the corallite walls, are quite sharp and somewhat thin, handling during collection and shipping can easily damage this skeleton material and associated tissue. It's always better to select a specimen that looks healthy and shows no signs of damage or tissue recession, nor has any kind of alga growth (brown or green) on any exposed skeleton surface.
And do not remove a specimen with fully inflated bubbles from the water, as the weight of the water on the bubbles may damage or tear its flesh. Gently shake the specimen and allow the bubbles to retract somewhat before removing.