Bubble Coral

by B. N. Sullivan

Bubble coral on a Red Sea reefWe have displayed a lot of photographs of reef scenes on The Right Blue. Reefs are formed by corals. The stony corals in the order Scleractinia are the reef-building corals that secrete calcareous skeletons for their polyps, which accumulate over time to become the hard framework of reefs.

We have posted quite a few photos of different kinds of soft corals, ranging from 'broccoli coral' and other Nephtheids to sea fans. Soft corals generally are more colorful and showy, and so they often are more attractive subjects for photography, but without hard corals, there would be no coral reefs. Until now, we haven't really focused much on stony corals, so we thought it was time we introduced some of the more interesting ones to readers of The Right Blue.

Some hard coral colonies form massive lumpy structures that look much like rock. Other stony corals form into fingers, pillars, antler-like branches, or even structures that look like plates. The ridged ones commonly referred to as 'brain coral' belong to the stony coral group, too.

Bubble coral vesiclesOne of the more unusual-looking stony corals we know about is Bubble Coral, an organism in the family Caryophyliidae. The first photo on this page shows a large colony of Bubble Coral on a reef in the Red Sea. If you click on the photo to enlarge it, you will see clusters of what look like bubbles -- thus the common name. Those bubbles, or 'vesicles' as they are properly called, are little balloon-like structures with rubbery skin that inflate during the day.

At left is a macro photo of the vesicles. The species in these photos, Plerogyra sinuosa, is quite common in the Red Sea. Usually it is found on steep slopes or on the vertical walls of underwater cliffs at depths of about 15 meters (50 feet) to about 40 meters (130 feet). I shot the first two photos on this page at Ras Mohammed, a well-known reef at the tip of the Sinai Peninsula.

I took the third photo on this page during a night dive off the coast of Tiran Island, which is situated at the mouth of the Gulf of Aqaba. Although we are not 100% certain, we believe that the organism in the photo is Bubble Coral of the same species as the photos above. Unfortunately, we did not get to return to the same spot in daylight to verify that this was indeed Plerogyra sinuosa.

Plerogyra at nightAt night, Bubble Coral looks very different than it does during daylight hours. The Bubble Coral's vesicles deflate, exposing its tentacles and its mouth.

In the photo at right you can see what appear to be the partially deflated vesicles, as well as the little tentacles. The tentacles can sting.

By the way, the vesicles of this species usually are whitish, often with striations of grey or very pale blue. They are translucent, and can look slightly opalescent. We have seen Bubble Coral elsewhere with a golden or greenish tinge. Next time we'll show you some more Bubble Coral, this time from Indonesia. The Bubble Coral we saw there had some 'extras' that led us to think of it as Bubble Coral Plus.


  1. Wow - a big difference in the night and day photos - when does it feed - when they are inflated or deflated?

  2. Well, as I said, we're not 100% certain that the last photo is Bubble Coral at night, but it strongly resembles a photo we saw elsewhere that was identified as Bubble Coral at night.

    I believe they do feed primarily at night, when the bubbles are deflated and the tentacles are exposed.


  3. I would have said the top photo showed the broccoli coral until I enlarged it, like you suggested. From a distance it looks like a produce counter to me!
    Thanks for explaining how the "bedrock" of reefs is formed.

  4. Hi Lavender -

    I'm chuckling at "produce counter." Funny how everything seems to look like something else more familiar. I guess that's how our poor brains make sense of unusual things.


  5. I clicked on the 1st photo to see the bubbles as you suggested and my 7 year old jumped across the couch and almost sent my laptop flying. Why, you ask? One of the fish in the picture is a parrot fish. He just completed his first ever research paper and it was on parrot fish! He was excited to see one on your blog. The boys all enjoy looking at your pictures.


We welcome your comments and invite your questions. Dialogue is a good thing!

Bobbie & Jerry