Propagating Hammer Coral (Euphyllia ancora)

How to frag hammer coral, Euphyllia ancora, covering the difference between easy branching morphs and harder wall colonies, plus sweeper-tentacle and brown-jelly risks.

Overview

Hammer coral, Euphyllia ancora, is a large-polyped stony coral of the family Euphylliidae, recognizable by the hammer- or anchor-shaped (T-shaped) tips on its tentacles. It occurs through the tropical Indo-West Pacific from the Maldives to the Solomon Islands, with large populations in Indonesia. Colonies form either flabello-meandroid (wall) or phaceloid/branching structures, and they host symbiotic zooxanthellae acquired during larval development.

Reproductive Mode

In nature the species is gonochoristic and reproduces by external fertilization, while new colonies can also form from detached tentacle tips. In the aquarium, propagation relies on asexual division of the colony, and the difficulty depends heavily on whether the colony grows as a branching head cluster or as a solid wall.

Fragging / Asexual Propagation

Branching hammers are the easier morph to frag: individual heads sit on separate skeletal branches and can be cut between heads, usually without slicing through flesh. Wall hammers are slower-growing and harder to frag because dividing the colony means cutting through the continuous wall and its sensitive tissue. Cut each head with its own piece of skeleton and allow it to recover.

1. Use sterile bone cutters or a rotary tool, with gloves and eye protection.
2. On branching colonies, cut between heads along the skeletal branch, keeping skeleton under each head.
3. On wall colonies, expect to cut through the wall and minimize the number of cuts.
4. Dip the frags, mount them, and place in adequate flow to heal.

Conditions for Propagation

Hammer corals recover under moderate (about 100-150 PAR) lighting and lower-to-moderate flow, with stable alkalinity, calcium, and magnesium and low nutrients. A healthy frag shows a thick flesh band around the skeletal edge and fully extended, well-defined tentacles once settled.

Sexual Reproduction

Sexual reproduction in Euphyllia ancora is broadcast spawning: in Taiwan populations a mass spawn occurs in late spring, synchronously on the third and sixth nights after the full moon during neap tides. Captive sexual reproduction is not a practical propagation route for hobbyists, who rely on fragging instead.

Common Challenges

Euphyllia deploy long sweeper tentacles armed with stinging cnidocytes, so frags must be spaced away from other corals they could reach and sting. The most serious post-fragging threat is brown jelly disease, which can kill an affected colony within weeks and spread to others; avoid specimens already showing a brown gel-like coating.