Acropora humilis

Description: All Acropora spp. corals have very porous and lightweight skeletons near the edges of the coral and the tips (branches). The bases, on the other hand, are very dense.

These corals are characterized by fast growing terminal (or axial) polyps at the tips of the branches. These terminal polyps do not have zooxanthellae. They grow quickly because the terminal polyps are fed by the rest of the colony. This allows Acropora to outgrow other corals on the reef.

Acropora are found in a great range of colors - blue, pink, purple, orange, green, yellow. Many have golden-brown structures with pale tips in white, pink, purple, blue, or green.

Acropora humilis is a Cluster or Corymbose Acropora. The branches of this coral are thick and taper to a dome shape, looking similar to fingers, hence one of it's common names. There will be larger branches mixed in with smaller ones. Radial corallites (the cup formed by a polyp) are found in two sizes, the larger ones in rows but increasing slightly in size towards the base of the branches.

Background: Acroporas are from the Subclass Zoantharia and the Order Scleractinia. The family Acroporidae was erected by Verrill in 1902. The scientific name Acropora spp. is credited to Oken in 1815.

As a whole, the many Acropora spp. corals are commonly called simply Acropora. The individual Acropora corals have many common names, usually based on their growth forms. Some of the common names include staghorn, cat's paw, bottlebrush, table, tabletop, finger, and so on. These common names are often used on many different species of Acroporas which can quickly result in confusion.

Quick Ref Chart
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Aquarium Care: Acropora need to be carefully acclimated to their new homes. They need to be placed in their permanent position within a tank after acclimation. Moving Acropora from place to place will stress them.

Excellent and stable tank conditions are required to keep all Acropora spp. corals. Tanks should offer high calcium levels and strontium should be added. A mature tank (well over a year old) is advised to increase the chance of successfully keeping Acropora.

There are many animals that will prey on Acropora spp. corals. Some Acropora have symbiotic relationships with crabs and shrimps that may help them against predators. Other hitchhikers may actually be predators so careful observation must be done.

Many Acropora spp. corals have been propagated by fragmentation. It is not difficult to find captive-bred colonies of this species of corals for sale or trade. Captive-bred corals may tolerate less intense lighting and water movement as well as possibly being easier to care for than those taken from the wild.

Lighting: High / Intense. Acropora humilis are found on the upper, shallow, portions of the reef and reef flats.

Water flow: High. According to Eric H. Borneman in Aquarium Corals: Selection, Husbandry, and Natural History, "... all Acropora seem to prefer a strong, random, mixing-type current ..." therefore a rotating powerhead or wavemaker setup is recommended. Acropora humilis are found on the intertidal areas of the reef where there is good water circulation.

Difficulty of Care: In the wild, these corals are found across the reef in various locations from turbid waters (with sediment or foreign particles stirred up or suspended in the water) to those with strong waves and high currents; from areas where there is little light to being fully exposed to the sun (and the air) at low tide.

With their natural habitat an array of conditions, it is surprising to find that these corals are among the more difficult to keep in captivity. They require stable tank conditions - sudden changes may result in death. They are sensitive to temperature changes, sedimentation, chemical and other environmental stresses. They do not tolerate being moved around in the tank.

Signs of stress are bleaching and receding and they will diminish and die rapidly. They are also susceptible to almost every coral disease including white-band disease, black-band disease, necrosis, etc. Acropora is particularly susceptible to rapid tissue necrosis (RTN), especially specimens from the wild.

Transporting Acropora spp. corals can also be a problem because of their shapes, the easily broken outer edges of the coral skeleton, and the ease with which they become stressed.

Availability: Acropora humilis is not a readily available coral for sale at most online retailers. However, it can be found, and prices vary based on size and color. Prices range from $25.00 to $70.00.

by Elizabeth M. Lukan, November 2, 2005

author of:
Fish'n Chips Newsletter
"Free monthly marine newsletter for saltwater tank hobbyists."