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How to keep bubble corals

Bubble corals are popular among reef aquarium keepers as not only are they eye-catching, they are also very hardy and easy to keep as Bob Goemans explains.

Copyright © Practical Fishkeeping

Bubble corals are among the most interesting stony corals, simply because of their appearance. Once you’ve seen a Bubble coral, its common names appear quite fitting because its skeleton mass is topped by an array of water- filled bubble-shaped polyps (vesicles).

Add to its eye-catching appearance the fact that they are very hardy and easy to care for, and it becomes quite clear why they are a favourite of many reef aquarium aquarists.

Bubble corals come from the Western and Indo-Pacific Oceans and also from the Red Sea. They are in the Phylum Cnidaria (Stony Coral), Order Scleractinia, Family Caryophylliidae, and are in the Genus Plerogyra. They are usually found in the wild in shaded protected areas that receive gentle water movement.

In these areas, eg. lower reef slopes, they are found under overhangs and cave walls, often in a vertical position. The waters are sometimes quite murky or turbid.

Even though there are two other described species (and possibly some yet undescribed) in this genus, ie., P. lichtensteini (usually called Pearl coral) and P. simplex (sometimes referred to as ‘branching’ Bubble coral), they are rarely ever seen in the trade.

The Bubble coral’s skeleton develops a flattened, continuous and unbranched wall of fused vertical plates (septa). It’s topped with a tissue mass having water- filled bubble-shaped polyps, which can develop slightly different shapes and colours.

Surface areas of the bubbles contain zooxanthellae and the bubbles expand during the day and mostly retract at night. At night, the coral displays long sweeper tentacles, sometimes 7.5–10cm/3-4” or longer in length that can sting downstream neighbours within reach. They are also capable of stinging human flesh!

Bubbles are usually 1–2.5cm/1/2–1” long, occasionally larger and tapered feeding tentacles emerge at night to capture plankton.

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. Specimens over 1m/4’ across have been seen in the wild.

Where most aquarists are concerned, there is generally only one species of interest – Plerogyra sinuosa (Dana, 1846). The most common colours are white or light tan, yet some specimens exhibit a pale green or pink tinge depending on area of origin.

Those with coloured tints require slightly better lighting than white or tan specimens. Some bubbles have a fingerprint pattern on their surface, or a shimmering band down the middle area of the bubble, called Cat eye bubble corals.

It is thought that bubble size regulates the amount of light its zooxanthellae receive, since this coral does not photoadapt, which means it is incapable of adjusting its level of photosynthetic cells to match light intensity. It simply regulates how much light energy it captures with bubble size, therefore where you place them in the aquarium is extremely important.

Most prefer low to medium light, such as from fluorescent lamps. I recommend it does not receive ‘strong’ direct light from metal halide lamps and that you place it in the aquarium in a low light area first to prevent ‘light shock’. As it adapts over the coming weeks, move it to a brighter area.

Picture by Nick Hobgood, Creative Commons.

Nourishment
Even though Bubble corals are a photosynthetic stony coral, it is also a suspension feeder and therefore will accept meaty type foods when its feeding tentacles are displayed.

If feeding tentacles are displayed when I feed my aquarium, I use a small turkey baster and dose the polyps/tentacles with meaty foodstuffs such as fortified brine shrimp, mysis, diced clam/marine fish flesh/shrimp flesh, and/or products containing Cyclop-eeze or similar products.

Overfeeding, or feeding with large pieces of marine flesh, causes specimens to experience odd shape changes that might affect longevity, so feed sparingly, no more than twice monthly.

If 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. It’s also possible a strong current might separate the flesh from its skeleton.

Making more
It is possible for a clone of the specimen to form in the aquarium. A small growth or ‘bud’ will appear on the animal’s flesh, usually near its lower edges. Over time, this bud develops a tiny skeleton and from the weight of its forming skeleton, it drops off the parent. If cared for, this can now develop into an exact copy of the adult coral.

I’ve had a similar ‘budding’ occasion with a yellow leather coral where a few dozen buds formed on its backside. Some dropped off and were placed in secure areas in the aquarium where they began to develop into full replicas of the parent.

Another form of cloning happens when the tissue of the parent begins to spread onto a piece of substrate that the parent is touching and, as it does so, a skeleton begins to form inside the spreading tissue and a new Bubble coral begins! Unfortunately, both of these reproduction methods are quite rare in closed systems.

When shopping for a Bubble coral, be aware that the animal’s septa, ie., the upright large blade-like structures that extend above the corallite walls, are quite sharp and thin. Handling during collection and/or shipping can easily damage this skeleton material and its associated tissue.

Select a specimen that looks healthy and shows no signs of damage or tissue recession, or with any kind of algal growth (brown or green) on any exposed skeleton surface.

If algal growth is present, chances are slim that the coral will survive as algal encroachment is often unstoppable. Do not remove a specimen from the water with fully inflated bubbles as the weight may damage or tear its flesh. Gently shake it to allow the bubbles to retract a bit before removing.

Health
A possible downside is a more or less naturally occurring health problem with this coral called ‘brown jelly’ infection. These jelly-like masses, consisting of the protozoan Helicostoma nonatum and bacteria, feed upon damaged/dying tissue.

Their toxins kill adjacent healthy tissue, and they then feed upon the new dying tissue and the march goes on until the entire specimen dies, usually within a day or two!

Generally, a healthy specimen should never incur this problem, but damage caused by hermit crabs/true crabs, shrimp, fish, or something falling against it, can set it off and, once it begins, it needs to be attended to immediately because of the speed at which it spreads.

To overcome this situation once started, I prepare a well-mixed litre solution of aquarium water containing 8 drops of Lugols iodine. I also have a small holding container (hospital tank), such as a glass fish bowl or small aquarium, just large enough to house the cleaned specimen.

This is filled with aquarium water that has 4 drops of Lugols iodine added to it per gallon. It has no substrate, but does contain a small powerhead for circulation and is moderately lit.

Once fully prepared, I remove the infected specimen from the aquarium and, over an empty bucket, use a soft brush and the prepared litre solution to remove as much brown jelly as possible. I then use a turkey baster filled with the remaining 8-drop solution and squirt only those brushed areas, while continuing to hold the specimen over the empty bucket.

It is then placed in the hospital tank, which should have the same pH, specific gravity, and temperature as the aquarium. It remains there, with 10% water changes (using water from the show aquarium) every other day until the brown jelly infestation has stopped. If necessary, I’ll repeat the cleaning process. I’ve found the sanitising effect of the Lugols often quickly halts the invasion of brown jelly.

Poor water quality can result in inadequate formation of new skeleton material, or its growth may simply not keep pace with upper tissue growth. This can lead to the tissue detaching and barren skeleton sections becoming coated in algae.

Pay attention to calcium and magnesium levels (as with all stony corals) and maintain in acceptable ranges: calcium 380-430 ppm, and magnesium in a range that corresponds to the specific gravity (sg.) in the aquarium – about 1280 ppm if the sg. were maintained at 1.025-1.026. Alkalinity should be maintained at 3.5-4.0 meq/l, with pH 8.1-8.2, and phosphate < .05 ppm, with a temperature of 23–28°C /74–83°F.

This article was first published in the November 2006 issue of Practical Fishkeeping. It may not be reproduced without permission.

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Bob Goemans 1419 (words, 9488 hits)
Published online: 05.06.09


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