Care
Bubble Coral is an instantly recognisable species of large polyp stony (LPS) coral that is known from the turbid waters of protected reef environments, to depths of 40m (131ft). The common name reflects that of the unique bubble-shaped polyp extensions, which resemble broad beans or grapes when fully expanded; indeed this species is also sometimes referred to as Grape Coral. These euphyllids form flat to round colonies, with corallites raised on short, thick stalks. Their skeletons are flabello-meandroid, with large, wide, prominent septa that extend well past the corallite walls. Vesicles (polyp extensions) are the size and usually the shape of grapes but may be bifurcated, irregular, or tubular, depending on their state of inflation. These vesicles are zooxanthellae "accommodators", that, by inflation during the day, expose their internal zooxanthellae to more light (there is an estimated tissue/zooxanthellae surface area increase of around 500%). At night, the vesicles deflate, and tapered feeding tentacles extend, along with some sweeper tentacles. Bubble Corals may be brown, blue, cream, green, tan, or white in colour, some with a single translucent stripe through the bubbles (referred to as "cats eye bubbles"). Most specimens are found growing in caves and under overhangs, so it is important that they are not exposed to intense lighting in the home aquarium - moderate but indirect illumination is best. Water movement should not be too vigorous, as this will allow the coral to fully expand its vesicles during the day. If the current is too strong, there is also risk of the inflated vesicles being damaged as they are pushed against the sharp septa. The size of the vesicles is directly proportionate to the amount of light and current the coral is exposed to. The dimmer the illumination, the larger the vesicles, as they expand to expose their zooxanthellae to the maximum amount of light that is available. Careful positioning is necessary with Bubble Corals, as they will extend potent sweeper tentacles at night (these may be several inches long), and these are capable of damaging most other neighbouring corals on contact - be sure to leave a decent amount of space around the colony. Always handle the corals by the hard skeleton only, as the fleshy vesicles can tear/puncture fairly easily. As Bubble Corals are not incredibly common in the wild and are considered to be of Near Threatened status, always try to ensure you purchase maricultured specimens wherever possible, to take pressure off the reefs.
Feeding
This species is zooxanthellate, but it is a voracious feeder that will benefit from feeding with small meaty food items such as Mysis shrimp, vitamin-enriched brineshrimp, chopped clam etc. several times per week. When supplementing its diet with these meaty items, do keep a close eye on water quality. Target feed at night when the feeding tentacles are extended.
Propagation
Bubble Corals reproduce asexually via budding very successfully in the home aquarium. A small growth typically arises from the lower edge of the coral, and over time this growth will increase in size and then develop a small skeleton of its own. The larger it gets, the heavier it becomes, and eventually it will drop down and break away from the main colony, and will attach itself to the substrate. Sexual reproduction also occurs in the wild (where colonies release sperm and eggs simultaneously) but this is rarely seen in captivity.
