Sun Coral

The sun coral is a stony coral made up of bright orange corallites with yellow tentacles opening from them. It has one fundamental difference from most aquarium corals: its tissue contains no symbiotic algae (zooxanthellae), which means it cannot get nutrition from light. It gets all of its nutrition from food caught with its tentacles; if it is not fed regularly, it starves and wastes away within a few months. In the wild the polyps mostly open at night, but in the aquarium they can also open during the day as they get used to feeding.

Its care takes time, but since it needs no light it is a good way to make use of the shaded corners of an aquarium. Its trade is subject to CITES Appendix II; aquacultured colonies are becoming more and more common, so choose those. The species has spread as an invasive in the Atlantic (Brazil, the Caribbean, the Gulf of Mexico); never release the colony, its offspring or aquarium water into the sea or the wild.

Its native range is the Indo-Pacific, where it lives at cave mouths, under rock overhangs and on shaded vertical surfaces, in places where currents carry plankton. Because it needs no light, it also settles easily at depth and on artificial surfaces such as ships and platforms.

• Light: Not important; low light is preferred. In strong light the top of the skeleton becomes covered with algae.
• Flow: Moderate, enough to sway the polyps gently. Detritus should not collect, but strong flow makes feeding difficult.
• Placement: A shaded crevice, a rock overhang or a vertical surface; it must be easy to reach for feeding.
• Water parameters: Salinity 1.024–1.026, KH 7–10 dKH, calcium 400–450 mg/L, magnesium 1250–1350 mg/L. The real challenge is the nutrient load that heavy feeding brings; a strong protein skimmer and 10–15% water changes a week are needed.

It is not photosynthetic; regular feeding is essential. Every day or every other day, give each polyp mysis, chopped shrimp, fish flesh or brine shrimp individually with a pipette. If the polyps are closed at first, the scent of food in the water opens them within a few minutes; with regular feeding the polyps get used to opening at a set time. Siphon out uneaten leftovers right away.

It is a peaceful coral; it has no long stinging tentacles. Even so, tissue loss can occur at the border with a coral it touches directly; leave about 5 cm of space. It is itself easily harmed by aggressive LPS.

During feeding, cleaner shrimp and some fish may steal food from the tentacles; try to keep them away while feeding. Dwarf angelfish may pick at the polyps.

Well-fed colonies multiply on their own in the aquarium: new polyps bud from the sides of the corallites, and larvae are frequently released; these larvae settle on rock or glass and start new colonies. Large colonies can be divided with coral cutters.

• Polyps shrinking, tissue receding: The most common cause is starvation; increase the feeding frequency.
• Algae and cyanobacteria on the skeleton: Seen when there is too much light or food leftovers accumulate; move the colony to a shadier spot.
• High nitrate and phosphate: A side effect of heavy feeding; balance it with the skimmer and water changes.