Acan Lord

Known in the hobby simply as "Acan", this coral is one of the most colorful LPS. The colony is made up of polygonal corallites pressed against one another; the top of each corallite is covered with thick, velvety, fleshy tissue. The center and the rim of a corallite are often different colors, so the colony looks like a mosaic of colored rings. During the day the tissue stays inflated; at night short feeding tentacles emerge from each polyp.

Its former name is Acanthastrea lordhowensis; in the 2016 revision it was moved to the genus Micromussa, and both names are used in the hobby. Its close relative Micromussa amakusensis is easily confused with it in single-colored colonies. Its trade is subject to CITES Appendix II; aquacultured frags and farmed colonies are widely available, so prefer these.

• Rainbow Acan: forms that carry red, orange, green and purple tones together in a single colony.
• Ultra Acan: collector forms with sharp color rings that fluoresce strongly under blue light.
• Single-colored forms: red-, purple- or green-dominant colonies at more affordable prices.

It occurs over a wide area of the Indo-Pacific, but is most common on shallow reefs in subtropical regions, for example along the coast of eastern Australia and at Lord Howe Island. Here the water temperature is more variable than on tropical reefs; this explains the species' hardiness in the aquarium.

• Light: Low to moderate, about 50–150 PAR. Under too much light the colors turn brown or the tissue bleaches; the most vivid colors are seen under blue-dominant moderate light.
• Flow: Low to moderate and indirect. The tissue should sway gently; strong flow makes the polyps shrink and prevents night feeding.
• Placement: The lower part of the rockwork or a stone on top of the sand. On horizontal surfaces the colony grows in a spreading form.
• Water parameters: Salinity 1.024–1.026, KH 7–10 dKH, calcium 400–450 mg/L, magnesium 1250–1350 mg/L. Sensitive to sudden KH changes. Stripping nutrients down to zero thins the tissue; nitrate 2–10 mg/L and phosphate 0.03–0.1 mg/L are more suitable.

Photosynthetic, but makes very good use of food. Some time after the lights go out, the polyps extend their feeding tentacles; at this time mysis, brine shrimp or a fine-grained LPS food is released over the colony with a pipette two or three times a week. Regularly fed colonies put out new polyps faster and their tissue stays fuller. Feeding the polyps one by one keeps fish from stealing the food.

It does not put out long "sweeper" tentacles, but it can digest a coral it touches by releasing its mesenterial filaments onto it. So leave a gap of 5–10 cm between it and neighboring corals. It should not be placed within reach of aggressive species such as Euphyllia, Galaxea and Favites. Different Acan colonies can be lined up side by side, but tissue loss may be seen at the border where they touch.

Dwarf angelfish, some large angelfish and hermit crabs may pick at the fleshy tissue. Bristle worms do not attack healthy tissue but may gather on damaged areas.

It is propagated by cutting between the corallite walls with a diamond-blade saw or sturdy coral cutting pliers. Even a single polyp can survive as a frag, but pieces with several polyps recover faster. After cutting, the pieces are kept in low flow for a few days. New polyps bud at the edge of the colony; because growth is slow, reaching a large colony takes years.

• Tissue recession: tissue loss starting at the edges usually comes from too much light, KH swings or contact with a neighboring coral.
• Brown jelly: if a slimy brown layer appears, separate the affected polyps and give a coral dip.
• Mouths staying open: swollen mouths that stay open during the day are a sign of stress; check the light, flow and water parameters.