Duncan coral care

Quick reference

What is a Duncan coral?

Duncanopsammia axifuga is a colonial stony coral of long, irregularly branching tubes, each topped by a large green or blue-grey polyp whose tentacles stay out day and night and can hide the skeleton completely.^[8] It's found mainly off Australia, with recent records from East Timor and West Papua,^{[1, 9]} and Corals of the World says it usually lives below 20 m, attached to hard substrate in areas dominated by soft sand.^[8]

It belongs to Dendrophylliidae, a family of mostly non-photosynthetic corals that includes the sun corals (Tubastraea); Duncanopsammia is one of the few genera in it with zooxanthellae.^{[10, 11]} Even so, the Western Australian Museum calls it a voracious heterotrophic feeder.^[1] Care ratings vary: Bulk Reef Supply lists it among beginner corals, while LiveAquaria rates it moderate.^{[12, 4]}

Lighting for a Duncan coral

Low to moderate is the usual advice.^{[4, 16]} Numeric guidance runs from 100–200 PAR (Top Shelf Aquatics, which accepts 50–200) to 150–250 PAR (Bulk Reef Supply's listing for aquacultured ORA Duncans).^{[5, 7]} Practical Fishkeeping suggests keeping it out of the main beam of a metal halide.^[17] Start it low and raise the intensity over two to three weeks.^[5]

Flow and placement

Low to moderate, and indirect. Top Shelf says direct flow damages the tissue, and Practical Fishkeeping says it needs adequate flow but not the strong currents SPS corals get.^{[5, 17]} In the wild it sits on hard substrate near sand,^[8] so a rock low in the scape matches its habitat.

Feeding

Feed it. In a 2017 aquaculture study, brine shrimp (Artemia), plain or lipid-enriched, significantly increased growth and polyp production,^[2] and unfed single-polyp fragments grew at half to a third the rate of fed ones and produced no new polyps over the 100-day experiment.^[3] Retailers suggest target-feeding mysis, brine shrimp, zooplankton or chopped seafood two to three times a week; that frequency is their advice, not something the study tested.^{[16, 5]} Bulk Reef Supply notes it also takes pellets.^[12]

Aggression and spacing

Low. The Western Australian Museum calls it a relatively unaggressive coral and a relatively poor competitor, and Reef Builders says it has no sweeper tentacles: when a neighbour bothers it, it retracts and produces slime.^{[1, 15]} The risk mostly runs the other way; Practical Fishkeeping advises keeping it away from other LPS.^[17] We found no source giving how far its tentacles reach.

Tankmates

LiveAquaria calls it peaceful with non-aggressive corals and invertebrates.^[4] Large angelfish graze fleshy LPS and dwarf angelfish may nip them,^[18] and one Meerwasser-Lexikon user reported an Aiptasia-eating filefish nipping Duncan polyps, though another saw no problem.^[6]

Fragging and propagation

Easy to frag. Snap or cut individual branches at the base with bypass cutters or a bandsaw, then glue each to a plug with gel superglue or epoxy.^{[19, 5, 20]} Let the polyps retract before lifting the colony out of the water.^[20]

In the 2017 study, pieces of skeleton with no polyps at all regrew them, sprouting new polyps in about 20 days against about 60 days for single-polyp frags, with 85 % survival across treatments.^{[2, 3]} Old colonies crowd and shade themselves, which is a good reason to thin them.^[21]

Troubleshooting

Common mistakes

• •Treating it as purely photosynthetic and never feeding it.^{[2, 3]}
• •Strong, direct flow.^[5]
• •Moving it straight under high light without acclimation.^[5]
• •Placing it next to aggressive LPS; it's a poor competitor.^{[1, 17]}
• •Letting the colony crowd and shade itself instead of fragging it.^[21]

Equipment & food for this species

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Most LPS benefit from occasional target-feeding, and a dip on new frags catches hitchhiking pests before they reach the display.

Duncan coral FAQ

Do Duncan corals need to be fed?

They host zooxanthellae, but feeding is strongly recommended: in a controlled study fed fragments grew faster and made more polyps, and unfed single-polyp frags made none in 100 days.^{[2, 3]} Retailers suggest target-feeding two to three times a week.^[5]

Are Duncan corals aggressive?

Generally no. Reef Builders says they have no sweeper tentacles, and the WA Museum calls them a relatively poor competitor.^{[15, 1]}

How much light does a Duncan coral need?

Low to moderate. Numeric guidance ranges from 100–200 PAR (Top Shelf) to 150–250 PAR (Bulk Reef Supply). Raise light over two to three weeks.^{[4, 5, 7]}

How fast do Duncan corals grow?

Hobby sources call them fast-growing, but we found no reliable growth rate.^{[7, 17]} In one study, polyp-less frags sprouted new polyps in about 20 days, and feeding greatly increased growth.^[3]

How do you frag a Duncan coral?

Snap or cut a branch at its base with bypass cutters or a bandsaw, then glue it to a plug with gel superglue or epoxy.^{[19, 5, 20]} Even skeleton pieces with no polyps can regrow them.^[2]

Is a Duncan coral photosynthetic?

Yes. Unlike its relatives the sun corals, Duncanopsammia has zooxanthellae, but it also feeds heavily.^{[10, 11, 1]}