Bubble Coral Plus

by B. N. Sullivan

In the previous article, we introduced our readers to Bubble Coral (Plerogyra sinuosa), a type of stony coral recognizable by the inflated bubble-like vesicles that give rise to its common name. Sometimes other little creatures live in or on the Bubble Coral. We refer to that situation as Bubble Coral Plus.

For Wordless Wednesday, we posted a macro photo of Bubble Coral with a tiny shrimp (Vir phillipinensis) that makes its home among the Bubble Coral's vesicles. The first photo on this page shows another instance of Bubble Coral Plus. This time the Bubble Coral is host to an entirely different critter, the Waminoa flatworm.

The first time we saw Waminoa on Bubble Coral we thought it looked like some kind of algae growing on the surface of the vesicles. We found out only recently that the spots actually were tiny critters. Apparently not too much is known about these flatworms, except that they inhabit some soft corals, as well as the soft parts of the Bubble Coral, and once they are established, the reproduce rather quickly.

This second photo is a 1:1 macro shot. If you click on the photo to enlarge it, you'll be able to see that the Waminoa flatworms look like little pancakes clinging to the surface of the Bubble Coral vesicles. Apparently not a whole lot is known about the Waminoa flatworms, but it is thought that they in turn are host to tiny dinoflagellates -- single cell life forms that produce nutrients through photosynthesis, some of which they share with their host.

I took both of the photos on this page in the Celebes Sea at Bunaken Island. The little island is part of an offshore marine reserve near Manado, on the northern finger of Sulawesi Island in Indonesia. Most of the Bubble Coral in this area has a golden or greenish tinge to it, whereas most of the Bubble Coral we saw in the Red Sea was white, sometimes with a pale bluish tinge. We are not certain if the Bubble Coral in the Celebes Sea is the same species as that in the Red Sea, but it belongs to the same genus, Plerogyra.

Someone who commented on the Wordless Wednesday photo of Bubble Coral mentioned that she had been snorkeling for a long time, and had visited many places, but had never seen Bubble Coral. That was not surprising to us, since it is not usually found at snorkeling depths. We have seen Bubble Coral at many dive sites in the Red Sea, and in various places in the waters around Indonesia and Malaysia, but never at depths of less than about 15 meters (50 feet). Thus, it is unlikely that snorkelers would get to see it.