Description
Name: Acropora
Temperature: 24-26C
Flow: low-mid
PAR: 150-250æ
Water parameters: Nitrate 5-10 mg/l, Phosphate 0,05-0,08 mg/l
Feeding: They are adept feeders that can grab and consume a wide variety of foods ranging from coral-formulated sinking pellets to frozen food such as brine shrimp, mysis, and krill.
Care level: Easyæ
Location
Indo-Pacific - Acropora are a genus of small polyp stony corals found in reefs throughout the world including the islands of the Indo-Pacific including Fiji, Tonga, Solomon Islands, and the Great Barrier Reef. They grow branching colonies that take on a variety of forms ranging from stag horns, elk horns, or even flat tables. Acropora are one of the primary reef building corals and are responsible for a large percentage of a reefs structure.
Lighting
Most coral on the reef are photosynthetic and have some demand for light. Like many corals, Acropora have a special symbiotic relationship with dinoflagellates called zooxanthellae that live inside its tissue. The dinoflagellates are actually the photosynthetic organism and the coral animal consumes the simple sugars that are byproducts of photosynthesis. Zooxanthellae is usually brown in color and the coral tightly regulates the population living in its flesh. Too little light will cause the coral to turn brown in color. As it seeks more nutrition, the coral allows more zooxanthellae to build up in its body. Too much light and Acropora will expel the zooxanthellae making its overall appearance lighter in color. If a coral is particularly stressed it can expel nearly all its zooxanthellae as a last resort and cause unhealthy bleaching. Hobbyists looking to find that _just right” color play with both lighting intensity and spectrum over their tank.
There is a misconception in reef keeping that all corals require high lighting. In fact, very few corals need high intensity lighting and in many cases problems arise when there is too much light not too little. Acropora however are one of the few types of coral that are truly light loving. In our systems Acropora have fared best when given light intensity around 300 PAR however there are plenty of successful systems with lighting intensities higher than 500 PAR. Having said that, I don_t recommend blasting newly added Acropora with a ton of light right away. More damage is caused by overexposure to light intensity than not providing enough light so take a couple of weeks to allow the coral to adjust to lighting conditions in your tank.
Water Flow
Acropora are found in some of the strongest current areas of the reef and benefit greatly from strong water movement in the home aquarium. Water movement is essential for bringing nutrients to coral and more importantly removing waste away from them. Acropora even grow in patterns to adapt to the flow in a given area. For example, Acropora in very strong flow grow thicker and more dense than in tanks with less flow. Some species of Acropora might even take on a stockier shape with fewer long branches in very high flow areas.
The growth of the colony in relation to flow also plays a part in their nutrition. They might be growing in such a way to maximize bacterial growth between the branches. One publication that I found interesting was from Coral Reef in 1989 by Schiller and Herndl. Basically it took a look at the interstitial space around certain SPS. They looked at a few different parameters such as ammonia, nitrite, nitrate, phosphorous, and bacteria levels between the branches on the interior of the colony compared to the ambient water column. What they found was that there were lower concentrations of dissolved organics in the interstitial space with an associated uptick in the concentration of bacteria.
The corals may be feeding on bacteria directly or indirectly attracting microbe-feeding zooplankton that they then trap and consume, but it is interesting that the corals studied grow in a fashion that optimizes flow through the branches to maximize bacteria farming opportunities.
When trying to provide adequate flow there are two things over time that dramatically affect the performance. The first is the growth of the colony itself. Successfully growing Acropora quickly comes with the downside of the coral being a victim of its own success. Large colonies cut down flow significantly and over time choke off flow to other nearby colonies or even to the inner parts of itself. As colonies get larger and larger, it is important as hobbyists to pay close attention to changing flow demands and consider adding more flow or pruning the colony.
Secondly, you may notice that there isn't quite as much flow as you once had when everything was freshly installed. Other organisms love to grow in and around the aquariums pumps and plumbing. For this reason I recommend taking apart pumps and powerheads regularly for servicing. It does not take very much growth or blockages to greatly limit water flow output.
Water Cleanliness
As far as water cleanliness goes, two parameters to keep low are nitrate and phosphate. Elevated phosphates can lead to poor coloration and possible algae issues. Nitrate is an indicator of poor water quality and can cause stony corals to crash altogether if not lowered. The natural sea water levels of nitrate are between 5 ppm and 40 ppm. For Acropora, it is best to be on the lower end of that range. Phosphate levels should be much lower (around .01 ppm) but I would caution hobbyists that are looking to keep those two parameters as close to zero as possible. Nitrate and Phosphate are not bad in and of themselves. Elevated levels of them can cause problems, but they are absolutely required for biological processes in coral and cannot be produced through photosynthesis.
Feeding
We talked earlier of Acropora nutrition when we talked about lighting, but their requirements extend beyond their relationship with zooxanthellae.
Although a high percentage of Acropora nutritional requirements are acquired by photosynthesis, they also benefit from regular feeding for both growth and coloration. There are three great sources of food that work well, amino acids, small zooplankton, and simply having fish present.
Starting with amino acids, they are simple organic compounds containing a carboxyl (COOH) group and an amino group (NH2). To quote every high school biology text book, they are the components of proteins that are the building blocks of the cell. In addition to their role building proteins they are also necessary for other biological functions such as neurotransmitter transport and biosynthesis.
The amino acids needed vary on a species by species basis but practically speaking it makes little difference in the long run because even if certain amino acids go un-utilized by a certain Acropora they will be taken up quickly by another organism for their biological process.
