Hammer Coral

The hammer coral is one of the most popular large-polyp stony corals (LPS) in the marine aquarium. The tip of each tentacle widens like a flattened hammer, an anchor or the letter "T"; when the colony is fully open the skeleton disappears from view and a soft mass of tentacles sways in the current. Most colonies sold are the "wall" type: the skeleton is a single, meandering body spreading out like a fan. Its branching relative is a separate species (branching hammer).

Its scientific name changed with a molecular study published in 2017: hammer, frogspawn and their branching species were split into the genus Fimbriaphyllia, while the torch coral stayed in Euphyllia. The name "Euphyllia ancora" is still common in the hobby. Like all stony corals, its trade is subject to CITES Appendix II; choose an aquacultured frag or a maricultured colony instead of a wild-collected one.

• Gold hammer: Yellow-gold tentacles.
• Green hammer: Neon green tips; the most commonly sold color.
• Purple hammer: Forms with purple or pinkish tips.

It lives from the Indian Ocean to the Western Pacific on shallow reefs moderately exposed to waves and on horizontal rock surfaces. In some places it forms carpets several square meters in size, but a single colony rarely exceeds one meter. It is used to variable flow and water that occasionally turns turbid; this is why it likes moderate light and indirect flow in the aquarium.

• Light: Moderate light, about 75–200 PAR. Place a new colony in the lower-middle zone first and move it up over a few weeks; in excessive light the tentacles shrink and the color fades.
• Flow: Moderate, indirect and variable. The tentacles should wave gently; strong, one-directional flow tears the tissue and makes the polyps close.
• Placement: In the middle zone of the rockwork, on top of a solid ledge. There should be no other coral below or beside it.
• Water parameters: Salinity 1.024–1.026, KH 7–10 dKH, calcium 400–450 mg/L, magnesium 1250–1350 mg/L. Its greatest sensitivity is to swings in KH and temperature; daily KH fluctuation should not exceed 0.5 dKH. Its tissue is fullest when nitrate is around 2–10 mg/L and phosphate around 0.03–0.1 mg/L; it fades when nutrients are near zero.

It gets most of its nutrition from the symbiotic algae (zooxanthellae) in its tissue. In addition, it catches plankton and leftover food from the water with its tentacles. If you turn the flow down for a few minutes once or twice a week and offer mysis, chopped shrimp or fine-grained LPS food close to the tentacles, its growth speeds up noticeably. The hammer does not always bring food to its mouth right away; feed small amounts without forcing it. It survives without any feeding, but grows slowly.

It is an aggressive coral. Although its tentacles look short during the day, at night it puts out stinging "sweeper" tentacles that can reach about 15 cm from the skeleton; the tissue of any coral they touch dies. Leave at least 15 cm of space in every direction, and take into account which way the current pushes the tentacles. In most aquariums it is seen to sit next to frogspawn and other Fimbriaphyllia species without problems, but this is not guaranteed; the torch coral, on the other hand, does burn the hammer, so keep these two apart.

Clownfish sometimes adopt the hammer as a host; constant rubbing can wear the colony down. Dwarf angelfish, butterflyfish and some hermit crabs may pick at the tentacles.

Because the wall-type hammer has a single-piece skeleton, it can only be divided with a diamond-blade saw or a coral cutting tool. The cut is made through the bare skeleton between two polyp heads, touching the tissue as little as possible. The cut pieces are rested for a few days in a spot with low flow and moderate light. Since the branching species (Fimbriaphyllia paraancora) is much easier to propagate, it is usually preferred for frag production.

• Brown jelly: A brown, slimy layer forms on the tissue and spreads quickly. Remove the affected part immediately, rinse it in saltwater outside the aquarium and give it a coral dip.
• Rapid tissue recession: In recent years, fast tissue loss of not fully understood cause has been reported in Euphyllia and Fimbriaphyllia colonies. Observing a new colony in quarantine for a few weeks reduces the risk.
• Tentacles not opening: Usually due to strong flow, KH swings, a sudden increase in light or the chemical effect of a nearby coral.