by Editory on 2nd December 2016 in Corals & Invertebrates, Marine
Acropora Corals are one of the primary reef builders in our world’s oceans and they are highly sought after by experienced reef tank hobbyists for their remarkable growth rates and intense colours. As hobbyists the first thing that comes to mind when thinking of SPS corals is Acroporas.
Corals of this genus are without a doubt some of the most vibrantly colourful corals available for reef tanks today. They can be found in reds, blues, greens, purples, pinks, yellows, and many more, not to mention the variety of contrasting colors between established branches, growing tips, and even polyps. Acroporas also come in a variety of growth forms such as table, bottlebrush, stag horn, branching, bushy, and more. These two traits of colour and form give rise to an incredibly diverse group of corals at least in appearance. Fortunately, care requirements are similar for most members of the Genus. Almost all corals of the group are very easy to frag by removing a single branch and are fairly fast growing under ideal conditions, making them favourites for captive propagation and trading.
The genus Acropora has close to 400 nominal species with nearly half that many described. The majority of these corals are found in Pacific reefs, but 3 species are found in the Atlantic.
The most common name for Acropora corals is the popular “staghorn coral”. This is a branching form that fits many of the acropora species. There are many other forms that Acroporas take as well. Other forms are shaped like tables, plates, columns, ridges, bushes, fingers, or clustering corals. The table or tabletop Acroporas are some of the most elegant and sought after forms for very large aquariums. Yet they are also some of the most difficult Acroporas to keep.
Acropora corals are the largest, most contributing coral for reef formations in the world. In fact, between the Acropora and Montipora corals, they make up one-third of all reef building coral species. In the wild they are the most tolerant of water temperatures, salinity changes, water movement, and lighting, but in captivity they can prove to be very difficult to keep. In the ocean, they are the first to arrive at a reef and spread quickly.
Acropora species have been propagated in captivity, thus helping to conserve wild populations in the world’s reefs. Some of their growth forms have been included in common names such as staghorn coral, cat’s paw coral, bottlebrush coral, table coral, tabletop coral, and plate coral. Buying captive propagated Acropora Sp. also helps the aquarist. They are a bit hardier than their wild siblings, but they can still succumb to diseases typical to Acros. The polyps of most Acropora are small, so aquarists refer to them as small polyp stony corals, or SPS corals.
Acropora Corals in the Aquarium
Beautiful home reefs can be either a simple reef with hardier, less demanding species, or a more complex reef with higher maintenance specimens. Stony corals are more demanding and take a more dedicated effort. So keeping stony corals is itself a step beyond a simple or beginner reef.
Due to the more stringent requirements, keeping Acropora corals is not recommended for beginners. They are the most sensitive corals when it comes to temperature changes; and they stress very easily if the light is too low, or the water movement is not sufficient. Even moving them around the tank can cause them to stress and die. The Acropora coral likes medium to strong water movement, and prefers a turbulent flow. It requires strong light from VHO or metal halide. It is vital that their requirements are met along with maintenance of calcium, strontium and trace elements.
It takes about 5 to 6 months for Acropora species to regain their normal growth rates after being added to an aquarium. At times a healthy system has an additional Acro added and all the others die from polyp bail out or what people refer to as RTD (rapid tissue degeneration) and a whole tank of acros can be wiped out within a matter of hours. They are unsure why this happens, but it would probably be a good idea to have all the Acros you are going to want, and put them together at once while they are still young.
Brown, bottlebrush, and thin-branched Acropora are considered the most tolerant of aquarium conditions. Tabletop Acropora are the most difficult to keep in the home aquarium. The staghorn type, like Acropora formosa, are somewhere in between the two. 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.
Acroporas do best in a reef tank of 380 litres or larger, with some fish for organic matter production. Aquariums must be at least a year old, stable, and with very low nitrate levels. Provide high light levels (metal halides are suggested), a temperature range of 22.2 to 28°C, salinity (specific gravity) of 1.023-1.025, and a strong and surge-like water movement. They prefer a strong, random, mixing-type current, therefore a rotating powerhead or wavemaker setup is recommended. Tunze stream pumps, though they have a comparatively high initial purchase price, are popular with Acro keepers.
Pristine water conditions must be maintained. Doing water changes of 10% every 2 weeks is needed, although it is suggested that doing 5% water changes once a week will bring about amazing results. Keep the nitrate levels low. Suggested levels for Acropora species are:
Calcium: 400 to 450 ppm (closer to 450). If the Acro does not have enough calcium, it will not grow. There will be no tissue recession, but the polyps will be extended.
Alkalinity: 3.2 TO 4.5 MEQ/L (8 to 10 dKh – 10 is recommended)
Phosphates: 0, zero. Phosphates are the worst of all and all corals hate them.
Magnesium: 1350-1500. Magnesium makes calcium available, so if your calcium is low, check your magnesium levels before adding any more calcium.
Strontium: 10
See each individual coral for more information.
Acropora Coral Feeding
In the wild, Acropora corals have developed several feeding strategies to increase their survival in nutrient-poor waters. Acropora corals have a symbiotic relationship with a marine algae known as zooxanthellae, and they receive the majority of their nutrients from it. With zooxanthellae, many can subsist primarily on little more than sunlight, water, and oxygen. They have other feeding strategies as well, such as capturing planktonic organisms and ingesting microscopic food particles. This feeding is done at night, when the water moves, rising from the floor to the surface carrying particulate matter. They can also absorb dissolved organic matter, and the solitary bladder type corals can consume larger food particles.
In captivity, feeding zooplankton once a week is the preferred choice. Copepods, Artemia, and nauplii are too large for them to ingest. But new forms of prey are being developed, such as invert larvae and new strains of rotifers. Many feel that Acros in captivity need to be in a tank that has dissolved or solid organic matter to survive and thrive. Without this, they may seem fine for a while, but over a few months, without any visible indication, they may end up dead because of starvation. Signs of lack of food would be no new growth, polyps extending and some tissue recession.
Acropora Formosa
Compatibility and Social Behaviors
The Acropora corals are peaceful, but watch out for crabs. Many experienced aquarists do not believe any crab should be kept in a closed system with Acros. Crabs are opportunistic predators, with the exception some of the symbiotic crabs like commensal crabs, and gall crabs.
Acroporas are best kept in a small polyp stony (SPS) tank with only other SPS corals. They can send out digestive strands called ‘acontia’ that are actually used to digest neighboring corals, so keep an eye out for any problems. The exception to this would be if your system has an incredible filtration system and the Acros are at least 10″ away from other corals such as zoanthids, large polyp stony (LPS) corals, and other invertebrates.
Do not keep soft leather corals with your Acropora species as they are aggressive and release terpins that will eventually kill your expensive investment. Leather corals are dangerous to Acros, even in the best filtered aquariums. Some large polyp stony (LPS) corals can stretch out their tentacles and kill your Acros too, so caution is needed if you have a mixed reef.
Acropora Coral Reproduction
The Acropora Sp. are male and female and can reproduce both sexually and asexually. In the wild they reproduce sexually by releasing eggs and sperm at the same time, resulting in a fertilized egg, which then forms into a free-swimming planula larva. Eventually the planula larvae settles onto the substrate, becoming plankters. This then forms a tiny polyp, which begins to excrete calcium carbonate, and develops into a coral. Planula larvae are extremely vulnerable to predation, and very few survive. In the wild Acros reproduce asexually as well. The polyps at the tips of branching species secrete corallite around itself, forming longer branches. Acros also spread from breakage due to storms and fragmentation.
Propagation is rather simple for Acropora corals. First you need to choose a healthy coral that is not showing any signs of distress. Then, simply cut a branch at least 5cm long and glue the frag to a plug or rock. You can use the 2-part epoxy or underwater putties. A little tip, don’t glue frags upright since they will grow faster on their sides. The slime that the coral will exude should not come in contact with any other corals and gloves are suggested. Give the frag ample water flow.
Acropora corals can be maintained and grown well in marine aquariums. It is an important decision you need to make when you feel that you are ready and experienced enough to take them on. You may need to convert your tank and remove a lot of your old corals and restructure your live rock in order to accommodate your Acropora and their growth. It is the ultimate achievement in advanced marine reefkeeping when you can get Acropra coral to thrive in your aquarium and I must say it is well worth the effort!
Skittles Acropora Granulosa
The Kuhli Loach by Timothy Smith The Blind Cave Tetra – Astyanax mexicanum Tim Smith