Bubble Coral

Pearl Coral, Bladder Coral, Pearl Bubble Coral

Pearl Coral - Bubble CoralPlerogyra sinuosaPhoto © Animal-World: Courtesy David Brough

   Low light and gentle water flow is all you need to make this shiny Bubble Coral happy, if only all corals were this easy!

   The Bubble Coral Plerogyra sinuosa is commonly found in the aquarium trade. Called the 'Grape Corals', the Plerogyra spp. will actually inflate or deflate their water filled vesicles (bubbles) depending on the light available.

   The Plerogyra genus comes in branching varieties also. The bubbles on these corals can have little tips on the end. Hence the common name for one of the Bubble Coral's close relatives, the Pearl Coral or Octobubble Coral Plerogyra flexuosa.

   All the Grape Corals have lightweight skeletons consisting of short thick stalks topped with corallites. This skeleton is hidden by the oval water filled vesicle bubbles. These bubbles only come out during the day. At night they retract, making way for their tapered feeding tentacles to come out and gather prey. Be cautious, while the bubble do not have toxins, these feeding tentacles are capable of delivering a sting.

  The Bubble coral is easy to care for and not too pricey. This makes it a very desirable coral in any of its attractive colors. It comes in shades of bluish green to green, cream, and tan. In the wild, these corals form flat round colony clusters, looking much like clusters of grapes.

   P. sinuosa are quite content with low lighting and gentle currents.They can do well under stronger lighting too, as long as they are acclimated to it over a period of time. Feeding them regularly and being careful to not damage their tissue are the other two ingredients needed for success in keeping them.

Scientific name

   Family: Euphyllidae (Previously Caryophylliidae)
   Species: Plerogyra sinuosa

   The family Euphyllidae, "... is a very large family of zooxanthellate scleractinans, that were previously grouped in the family Caryophylliidae (Mather, 1994). It includes such genera as Euphyllia, Catalyphyllia, Nemenzophyllia, Plerogyra, and Physogyra." Source: Tropical Marine Biology II, Classification of Scleractinian (Stony) Corals, by Pierre Madl, University of Vienna, 2001, Revised in Nov. 2002

Distribution / Background

   Plerogyra Coral Information: The Plerogyra genus was described by Edwards and Haime in 1848. There are 6 nominal and 3 true species, but the two species that are most familiar are the Bubble Coral P. sinuosa and the Octobubble Coral P. flexuosa. Names these corals are known for are Grape Coral, Octobubble Coral, Bladder Coral, Pearl Coral, and Branching Bubble Coral.

   The Bubble Coral P. sinuosa was described by Dana in 1846. Some common names this species are known for are Pearl Bubble Coral, Cat's-eye Bubble Coral, Green Bubble Coral. They have been propagated in captivity.

   Where Plerogyra Corals Are Found: The Plerogyra genus are found in the Red Sea, Indian Ocean, and the west Pacific Ocean from the East China Sea all the way to the west, north, and east coasts of Australia, then east toward the Line Islands.

   Plerogyra Coral Habitat:The Plerogyra genus are found in gentle water movement on lower reef slopes, inhabiting caves or crevices, and under overhangs. They seem to have no real light preference. They can be found in low light areas that have almost total shade or in shallower brighter waters, yet all habitats have turbid waters.

Status

   The following species from the Plerogyra genus are on the IUCN Red List of Endangered Species:

• P. cauliformis: Data Deficient (DD)
• P. diabolotus: Data Deficient (DD)
• P. discus: Vulnerable (VU)
• P. multilobata: Data Deficient (DD)
• P. simplex: Near Threatened (NT)
• P. sinuosa: Near Threatened (NT)

Description

   What do Plerogyra Corals look like: Both the Bubble Coral P. sinuosa and the Octobubble Coral P. flexuosa come in one colony with large water filled "bubbles". This is a display that is easily recognizable. The "octobubble" term comes from the bubbles on the Octobubble Coral P. flexuosa, being "nippled" at the tip.

   The Branching Bubble Coral P. simplex has a similar look as P. sinuosa, except it has individual branches. These little groupings barely touch each other and are separated with quite a bit of space within the colony. P. discus looks almost identical to the Fox Coral Nemenzophyllia turbida, with the same flowery look, but each puffy vesicle is connected to a separate branch.

Green Bubble Coral
Photo © Animal-World:Greg Rothschild

   The Plerogyra genus, whether branching or not, has a typical lightweight skeletal structure that is easy to cut or sever. They have 1/2" to 1" (1 - 2.5 cm) vesicle bubbles that are oval and water filled, with a higher density of zooxanthellae than most symbiotic corals that have been studied to date. The bubbles are not polyps, but modified tentacles which protect the delicate polyps beneath them. The bubbles will expand or contract as needed for acquiring more or less light during the day, but at night they deflate. Then 3 - 4" (7.5 to 10 cm) feeder tentacles, which CAN sting, emerge looking for food. The small short tentacles sometimes seen with the bubbles during the day do not sting.

   The Plerogyra spp. come in shades of bluish green to green, cream and tan with lighter striations on the surface, but will turn brown if the light is too high. There are usually pieces of sharp, delicate, thin "bone" called septa in-between the bubbles. The tissue of the Plerogyra genus will actually connect and encrust onto nearby substrate. Some colonies can reach 3 feet (1 m) in the wild, but most are smaller, only getting to around 7.5" (19 cm). Their lifespan is unknown.

Difficulty of Care

   Plerogyra Coral Care: The P. sinuosa can be easy to care for. Needing only gentle water movement and low to moderate light, this is an easy LPS with few demands. When choosing your new charge, make sure the LFS employee gently shakes the coral until most of the bubbles deflate and recede. Removing it to air while inflated will cause tears in the flesh, leading to infection. Even if the coral is left submerged, the septa can cut into the bubbles against the bag it is being put into. Also, make sure there is no algae on the septa once it is visible.

Foods / Feeding

   Plerogyra Coral Feeding: In the wild, Plerogyra corals have developed several feeding strategies. Through a symbiotic relationship with a marine algae, known as zooxanthellae, they receive many of their nutrients. They also capture planktonic organisms, food particles from the water column, and can absorb dissolved organic matter.

   In captivity, feed when the feeder tentacles are out in the evening with mysis, rotifers, enriched brine shrimp, Cyclopeeze and other similar sized meaty foods. Try to not feed large pieces since it makes it difficult for the animal to digest such foods and often results in them regurgitating late at night. When this happens, they are not benefiting from the feeding and it can lead to eventual starvation.

Aquarium Care

   Typical water changes of 20% a month, 10% biweekly, or 5% weekly are needed. It has been noted that 5% weekly water changes replenish many of the needed additives and it is ultimately cheaper than purchasing additives for the water. With higher concentrations of coral with calcareous skeletons though, there may be a need put in additional additives to maintain proper levels for good growth.

   The following water supplements are suggested for Plerogyra species:

• Calcium:  380 to 430 ppm. If a large poly stony (LPS) coral does not have enough calcium, it will not grow. (Seachem makes a calcium additive that states 385 as sufficient)
• Alkalinity:  3.5 TO 4.8 MEQ/L (8 to 11 dKh, 10 is recommended)
• Phosphates:  0, zero. Phosphates are the worst of all and all corals hate them.
• Magnesium:  1200 - 1350. Magnesium makes calcium available, so if your calcium is low, check your magnesium levels before adding any more calcium.
• Strontium:  8 - 10

Aquarium Parameters

   A well-feed live rock/reef environment is what is needed for your Bubble Coral, along with some fish for organic matter production. A mature tank is recommended.

Quick Reference Chart
Lighting:
Water Flow:
Temperament:

   Provide gentle water movement and low to moderate light. Do not put under bright lighting.They can do well under stronger lighting too, as long as you slowly increase the intensity over time. Feed them regularly and be careful to not damage their tissue. Make sure that no other corals can come in contact with your Plerogyra as they are aggressive and will sting other corals.

• Minimum Tank Size / Length: 50 gallons (190 L) or larger
• Marine Lighting: Low or shaded Moderate light
• Temperature: 74° - 83° F (23° - 28° C)
• Salinity / Specific Gravity: 1.023 - 1.025
• Water Movement: Low / turbulent.
• Water Region: Bottom of the aquarium

Compatibility and Social Behaviors

   Plerogyra corals can be aggressive if touching other corals and should be positioned away from all other corals. It needs to be at least 6" away since it sends out sweeper tentacles at night. Their sweeper tentacles can punch a powerful sting to other corals as well as humans.

   Leather corals emit a toxin that will harm them. They have been known to die in the presence of a large leather coral population (Sinularia). The Plerogyra genus also does not like hermit crabs, as they irritate its flesh.

Sex - Sexual differences

   Unknown.

Breeding and Reproduction

   The large polyp stony (LPS) corals are male and female and can reproduce both sexually and asexually. In the wild they reproduce sexually by releasing eggs and sperm at the same time, resulting in a fertilized egg which then forms into a free-swimming planula larva. Eventually the planula larvae settles onto the substrate, becoming plankters. This then forms a tiny polyp which begins to excrete calcium carbonate and develops into a coral. Planula larvae are extremely vulnerable to predation, and very few survive. Plerogyras reproduce asexually as well.

   The tissue of the Plerogyra genus will actually connect and encrust onto nearby substrate and they tend to grow in a vertical orientation. At times, this results in a new "bud" and will start to form a new colony. Physical propagation should only be attempted on branching varieties. It needs to be left up to the encrusting behavior of this coral to propagate it. Cutting into the tissue will result in damage that can lead to disease. It is best to feed them well and keep them happy, then they will form buds which can be harvested and produce quite a few colonies a year! Just be patient. The larger your coral gets, the more "babies" it will give you.

   To propagate branching varieties, you first you need to choose a healthy coral that is not showing any signs of distress. Simply cut 2" or more from the head to avoid damage and glue the frag to a plug or rock. You can use the 2-part epoxy or underwater putties.The slime that the coral will exude should not come in contact with any other corals and gloves are suggested. Give the frag ample water flow.

Potential Problems

   The Plerogyra spp. are susceptible to a few maladies. Here are some of the most usual ailments:

• Brown Jelly
     Brown jelly or protozoan infections can infect the rest of the colony if not treated. This brown jelly looks exactly like it sounds, and can be caused by poor water quality and/or tissue damage. To treat, remove the coral to a container with water from the main display, then brush or siphon off any visible brown jelly. Give the coral a freshwater dip in water with the same pH and temperature as the main tank for several minutes to kill a lot of the microorganisms.
     Use an antibiotic paste on the infect areas and/or a Lugol's dip. Cyanobacteria and brown jelly infections can be treated with Neomycin sulphite, Kanamycin and other broad-spectrum antibiotics. The pill can be pulverized into a fine powder, mixed with sea water to make a paste, and then applied to the wound, or affected site of the coral with a simple artists brush.
     Try to treat the coral with the least stressful method first. Place in a quarantine tank until coral recovers.
• Flatworms
     Flatworms are another affliction that can be treated by a simple freshwater dip with the above parameters
• Algae
     If algae starts to grow on its septa, gently scrub it away, since the coral will not be able to recover on its own. An electric rotary tool can be used on particularly stubborn algae.
• Bright Lighting
     Tissue damage and shock will occur if placed under direct Metal Halides or other bright lights.

Availability

   Plerogyra Corals for Sale: The Bubble Coral P. sinuosa is very easy to find at pet shops and on line. Online they can run about $39.00 USD or more depending on size and/or color.

References

• Animal-World References: Marine and Reef
• Eric Borneman, Aquarium Corals : Selection, Husbandry, and Natural History , TFH Publications, 2001
• Anthony Calfo, Book of Coral Propagation, Volume 1 Edition 2: Reef Gardening for Aquarists, Reading Trees; 2nd edition, 2007
• J.E.N. Veron, Corals of Australia and the Indo-Pacific , University of Hawaii Press; 2 Rev Ed edition, 1993
• Ronald L. Shimek, Guide to Marine Invertebrates: 500+ Essential-to-Know Aquarium Species, Microcosm, 2005
• Eric Borneman, Do You Know Where Your Corals are Coming From? Ecological Information for Aquarists from Coral Collection Areas in Indonesia, Department of Biology and Biochemistry, Division in Ecology and Evolution, University of Houston, Part III, Advanced Aquarists Online Magazine, Copyright 2003
• Bob Goemans, Bubble / Bladder Coral, Plerogyra sinuosa, Animal Library, Saltwatercorner.com

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