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Acanthastrea is a relatively large genus in the family Mussidae, and consists of twelve species, all of which can be found in the areas where coral collection for the aquarium trade occurs, with the exception of A. maxima. Acanthastrea species are not easy to distinguish from several other genera, and even families, of corals. They resemble other Mussid corals, specifically Micromussa and Lobophyllia. They also resemble some species in the family Faviidae which has many genera and species that can be very difficult to tell apart.

In general, Mussids are corals characterized by large corallites with large teeth or lobes on their septa. The corallites generally have well developed columellae. In terms of knowing if a living specimen is a Mussid, it is possible to see or gently feel the septa for the presence of these large and often serrated-looking teeth. If they are not present, it is quite possible that it is a Faviid.

If the coral is determined to be a Mussid, one must measure the corallites across the diameter from wall to wall. Micromussa, which very much looks like Acanthastrea, has corallites 8mm or less. Acanthastrea generally has corallites smaller than Lobophyllia, and most have corallites between 8-15mm in diameter. Several species, though, can have larger corallites and these are the ones most difficult to distinguish from Lobophyllia and Symphyllia.

There is a reason for the above taxonomic distinctions, in that many aquarists may assume they have Acanthastrea in their tanks, and do not. In fact, several of the photos in this ReefSlides are questionable, and may be other species of other genera, including the faviid, Caulastrea. Because these corals have very fleshy polyps, being able to see the characters that would determine a positive identity are difficult to impossible, and even if Acanthastrea is the correct genus, assigning species in these living corals is very, very difficult.

With some exceptions, Acanthastrea are found in many locations on the reef, but are often from shallow water to about 20m in depth, and are frequently in somewhat protected locations. Some species, however, can be found much deeper. They can form colonies that are anywhere from a few polyps to large hemispherical to encrusting colonies several meters across, although not all species are likely to form such large colonies.

In the aquarium, as is typical for Mussids, they are tolerant of diverse conditions and can thrive in strong or subdued lighting and water flow regimes. They are voracious predators, and have strong nocturnal feeding responses. Additionally, they appear very competitive in their ability to extrude mesenterial filaments in a coordinated manner, similar to Hydnophora (as is seen in the last photo of this slideshow). An aquarist on Reef Central has provided photos of this behavior in The Coral Forum that make her colony appear related to SpiderMan. Therefore, care should be excercised when placing these corals near other sessile organisms that are desired to remain undigested by aggressive Acanthastrea.

Text by Eric Borneman.
Photos by Reef Central members.