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Tubular coral is a type of asymbiotic rocky coral. The term “tube coral” includes several species of the genus Tubastraea, which differs greatly from many other genera of rocky corals. Found off the coast of Fiji, the Solomon Islands, and Indonesia, this coral is also popular in home reef aquariums.
Also commonly called sun coral, sunflower coral, or cup coral, tube coral differs from most corals in many significant ways. Unlike most corals, whose small polyps secrete rocky skeletons that stick together, tube coral has large polyps that obscure the secreted skeletons. Also, instead of being found on the sea floor, coral tubes are more often found in underwater caves, suspended from the ceiling.
Most corals live in symbiosis with microalgae called zooxanthellae, which provide the coral with nutrients through photosynthesis. The tube coral lacks zooxanthellae and therefore needs to provide its own sustenance. Due to this independence, the tubular coral is considered symbiotic. Since it does not need photosynthesis to feed, it does not need light and is usually found where there is little light.
Tube corals capture their prey. Their main food source is zooplankton, small organisms that are carried by the ocean current. For this reason, tube corals always live in areas with strong currents.
Like all coral polyps, the tube coral consists of a tube-like structure attached to a surface at one end and topped by a mouth surrounded by tentacles at the other end. When the coral is not feeding, the mouth closes and the tentacles retract. The tentacles spread out and the coral resembles an anemone when feeding. Tube corals usually have orange tones, but one species of Tubastraea micranthus is black.
Popular in home aquariums, tube coral can usually be purchased in lengths from 5 to 13 cm. This coral can be stored in well-lit or dark places, since it does not need light or is affected by it. However, tube coral is considered a moderate challenge to the home aquarium owner, as its feeding requirements are unusual. Also, this coral normally feeds at night, although it can be trained to feed during the day, so its conspicuous tentacles can only be seen after dark.
Captive corals should be placed in an aquarium prepared to provide at least moderate currents. The coral is then fed with a dropper every night. Salt shrimp or plankton are common foods for these corals. Black tube coral is rare in captivity due to the strong current and the greater availability of food that it needs to feed properly.