The genus Acropora is one of the most species-rich of stony coral genera (while the number of species is debatable, there are more than 350 species in the genus). All of the acropora corals are important reef-building corals and often dominant huge sections of tropical coral reefs throughout the Indo-Pacific (they are also found on certain reefs in the tropical Atlantic, but there are few species in this region, and the species that are there are not nearly as abundant). While it was once only represented in marine aquariums by dead, bleached skeletons, now aquarists are successfully growing and propagating many Acropora species.
Difficulty: The Acropora genus has a mixed reputation, depending on the species and condition of the colony that you obtain. It is always best to go with aquacultured individuals. Even these colonies should only be added to more mature systems (more than 1 year old). Always select colonies that exhibit good polyp extension, and avoid those with any bleaching or tissue peeling. This coral relies on the zooxanthellae (algae) that live in its tissue to provide much of its nutrition, but zooplankton, nanoplankton and bacteria are also consumed by the polyps. They also absorb inorganic and organic nutrients from the surrounding water.
Physical description: The Acropora corals have been reported to exhibit at least 11 different growth forms (depending on the species and the environment they are living in). Colonies can be described as massive, encrusting, bottle brush, treelike (referred to as arborescent), digitate (short, fingerlike branches) and tablelike, to name some growth forms. They can also come in a rainbow of different hues, including purple, blue, pink, dark green, lime green and the all too ubiquitous brown (note: it has been suggested that the more drably colored individuals tend to do better in captivity). The colors can change in captivity — these changes have been attributed to changes in light intensity and quality, as well as diet. These corals grow rapidly, with branch growths of over 6 inches per year having been reported in some species.
Compatibility: The competitive advantage that these corals have over their sessile neighbors is that they grow very rapidly (an attribute that also makes them very popular with coral farmers). This can cause problems in the aquarium, as they will shade and grow into their neighbors. If you keep staghorn corals in your reef aquarium, be prepared with some bone shears, and don’t be afraid to do some serious trimming! These corals also have stinging tentacles and produce terpenes. These chemical can impede the growth of other corals (both stony and soft).
Aquarium conditions: Most of the Acropora species require a very high light intensity (from 5 to 10 watts per gallon). There are, however, some deepwater species (Acropora caroliniana, Acropora multiacuta, Acropora granulosa, Acropora lokani and Acropora suharsonoi) that can live under less intense light sources, but unfortunately these species are not readily available to hobbyists at this time. Moderate to strong water movement is also important to ensure their good health. Water parameters should be: calcium 400 to 450 ppm, alkalinity 3.2 to 4.8 meq/L, magnesium 1200 to 1350 ppm, no phosphates and a water temperature of 76 to 84 degrees Fahrenheit. Because it grows fast, it utilizes a lot of calcium. Monitor calcium levels and be prepared to add calcium supplementation frequently.
Care considerations: These corals suffer from a number of different diseases, including the dreaded rapid tissue necrosis. Always quarantine a new Acropora colony before adding it to your display aquarium to prevent the addition of some noxious parasite or disease. Hair algae can be this corals biggest enemy. These corals are also likely to bleach if exposed to sudden changes in light levels or sudden fluctuations in water parameters (e.g., pH, salinity).
Breeding: These are very easy corals to frag. Simply snap the end off of a healthy branch and attach it to a reef plug or piece of live rock.