Finger Leather Coral

The finger leather coral is a soft coral known for many years as Sinularia flexibilis and moved to the genus Sclerophytum in the recent classification of octocorals; in the hobby it is still mostly sold under its old name. Many thin, long, flexible branches rise from a short, thick trunk; the branches are covered with small polyps and sway in the current like the branches of a willow tree. Its color is usually cream, beige or light green.

It is a coral often recommended to beginners, resistant to disease and water fluctuations. Its problem is that it affects surrounding corals with the chemicals it releases into the water; this must be taken into account when setting up a mixed reef. It is not covered by CITES, and aquacultured pieces are common.

It lives in large colonies on shallow reef flats and reef slopes of the Indo-Pacific, in places with strong flow. In some areas it covers large parts of the bottom and limits the settlement of stony corals with its chemical defense.

• Light: Moderate light (roughly 100–250 PAR) is enough. It also adapts to low light, but its branches grow longer and thinner.
• Flow: Moderate and surging; a gentle swaying of the branches is enough. In harsh, constant flow the branches close up.
• Placement: The middle part of the rockwork; leave room above and to the sides for its crown, which widens as it grows.
• Water parameters: Salinity 1.024–1.026; KH 7–11 dKH, calcium 400–450 mg/L, magnesium 1250–1350 mg/L. Some nitrate (5–10 mg/L) and measurable phosphate do not harm its color or growth.
• Carbon: If it shares the aquarium with stony corals, replace the activated carbon every month.

It is photosynthetic; it gets most of its nutrition from zooxanthellae. Its polyps also capture fine particles from the water. It does not need to be fed separately; overfeeding only worsens algae problems.

It does not sting directly, but it releases terpene compounds such as flexibilide from its tissue into the water. These substances can stop the growth of SPS and some LPS and make their tissue recede, especially in small, closed systems. At least 20–30 cm of distance from stony corals, good flow, regular water changes and activated carbon are essential. It can be kept in the same aquarium as other leather corals, but they must not touch each other.

It is compatible with fish and invertebrates; some dwarf angelfish may pick at its branches.

It is one of the easiest leather corals to propagate. A branch is taken with a clean cut, attached to a frag plug with a rubber band or toothpick, and attaches within a few weeks. Doing the cutting outside the aquarium in a separate container keeps the mucus and chemicals released from the cut from reaching the main aquarium. The colony can also propagate on its own by dropping small branches.

• Drooping branches: After a new placement, a change in light and after cutting a branch, the branches droop and shrink for a few days; this usually resolves on its own.
• Waxy film: As with other leather corals, its surface is covered with a thin film from time to time and the polyps close; it recovers once the film is shed.
• Decline of surrounding corals: If unexplained fading or polyp closure is seen in neighboring stony corals, replace the carbon, increase water changes and, if necessary, remove the leather coral.