Acropora echinata

Acropora echinata builds colonies that resemble a bottlebrush, with thin branchlets arranged regularly around the main branches. The body is usually white or cream and the branchlet tips are blue or purple; entirely blue colonies are also seen. It is rare in the wild and vulnerable to ocean warming. Although its name technically clashes with an older name, it continues to be used because no replacement name has been proposed. Trade in stony corals is subject to CITES Appendix II; the known forms available in the trade are aquacultured, so choose only these.

• Hawkins Blue Echinata: A famous blue clone obtained from a hobbyist in Germany in 2006 and propagated in aquariums.

• Light: Moderate to high light; roughly 200–350 PAR. Because it comes from somewhat deeper water, place it not at the very top but in the middle-upper part of the rockwork.
• Flow: Strong but intermittent, random flow; no detritus should remain between the branchlets.
• Handling and care: Its protective mucus layer is weak; it should not be left out of water for long, and coral dips should be short and mild.
• Water parameters: Salinity 1.025–1.026, temperature 25–26.5°C and should not exceed 27°C, KH 7–9 dKH with daily swings below 0.5 dKH, calcium 400–450 mg/L, magnesium 1300–1400 mg/L, nitrate 2–10 mg/L, phosphate 0.02–0.08 mg/L.

It is photosynthetic; it gets most of its energy from zooxanthellae algae. Very fine powdered food or plankton given occasionally can support growth and polyp extension.

It is not aggressive; its thin branchlets are very vulnerable to the tentacles of neighboring corals, so leave 10–15 cm of space. Dwarf angelfish may pick at it; AEFW and red bugs are the greatest threat. Large hermit crabs and snails can break the branchlets.