By J. Charles Delbeek
Q. I have been into the marine hobby for about two years and have a 240-gallon fish-only tank, a 55-gallon reef and a 30-gallon modified Eng anemone tank. Some interesting developments have come about in the 55-gallon reef system.
I have a very nice octobubble coral that had a button-like coral growing on the lower part of the old skeleton. After a few months it became apparent that the "button" was some type of Fungia species. The thing grew until it reached about 3 inches in diameter. Today I noticed it had detached from its spot and is traveling down toward the tank floor. It left behind a button-size skeleton-like structure. Also, next to that is a small polyp on a stalk. I was wondering if these were offspring, as they had to be underneath the main individual.
In the same general vicinity is a large bubble coral. For the past few months this coral has not expanded fully, but it does not show any signs of disintegration. At times its mouth has been open very wide, so that I can see the structures within. At night it still extends tentacles, but not as fully as before.
My tank parameters are all normal. Nitrates are undetectable (low range test) and phosphates are 0.2 ppm, calcium is at 450 ppm. I have 440 watts of VHO lighting, two 50/50, one full sun and one actinic. I run a protein skimmer on this tank. There is extra circulation from a 403 Fluval (empty) in addition to what is circulated through the trickle filter and sump.
There are two kinds of red macroalgae algae that are flourishing. Green macroalgae is kept from growing by my four dwarf angels and a purple tang. I also have a herd of "reef janitors." What could be a probable cause of the bubble coral's depressed state?
A. The small coral you saw drop off was most likely a Fungia as you suspected. Planulae of Fungia species settle out and develop into a small structure called an anthocauli. The polyp grows in size while attached to the substrate until it reaches a size where it becomes large and heavy enough to break off from the attachment. At this point the coral is now a free-living polyp.
The small stalked polyp you found underneath your Euphyllia is most likely a daughter polyp. You can leave this attached or you can snap it off and reattach it elsewhere in the tank where it can get more light and grow faster. We covered both these types of structures in The Reef Aquarium, Volume One (1994).
As far as your bubble coral (Plerogyra sp.) not opening, there are a few possibilities. First off, your water chemistry sounds fine, so I do not suspect a problem there. Four Centropyge angelfish in a 55-gallon tank, however, are a lot of pygmy angels in a small area! These little "pickers" love to pick at rocks all day searching for food items, such as algae and small crustaceans. I suspect that what is happening to your bubble coral is that the pygmy angels are picking at it. All it takes is a few pecks during the day to keep the coral from expanding fully. The fact that it still expands at night is another clue that it is being harassed during the day.
As to what to do, I am afraid either the offending fish have to go or the coral does. Other possibilities include predatory worms in the rocks, a lack of food or excessive water movement. But I think that if you sat and watched the fish for a few hours, you would see them picking at the coral.