Acros Corals

The wide majority of Acropora Corals originate from the Indo-Pacific in major Reef Systems like the Great Barrier Reef off the coast of Australia.

Acropora is a genus of Small Polyp Stony Coral in the phylum Cnidaria.

The name Cnidaria comes from the Greek word "Cnidos," which means stinging nettle.

Some of its species are known as Table Coral, Elkhorn Coral and Staghorn Coral . Over 149 species are described Acropora are very easy to tell apart from most other Corals, but can easily be confused with other Small Polyp Stony (SPS) Corals.

It should also be mentioned that the appearance of any given Acropora can vary greatly depending on the conditions under which they’re being kept.

These differences can be in coloration and extension as well as subsequent movement and growth of the Coral.

These Corals are usually seen in branching forms in the wild as well, forming tight Acropora Colonies with relatively thick branches.

Other times, these branches can be very skinny and spread far apart and even come in Plating varieties.

In the more ornamental species, the flesh is often a bright color while the Polyps are highly contrasting.

Each Polyp has its own tube called a radial Corallite which can create a bumpy appearance.

The Polyps are usually very long, which can also create a fuzzy texture.

An axial Corallite is located at the end of each branch and appears to have a hole in the center.

These Corallites are used to distinguish different species of Acropora coral from one another.

Like other Corals, Acropora Corals are Colonies of Individual Polyps, which are about 2 mm Across and share tissue and a nerve net .

The Polyps can withdraw back into the Coral in response to movement or disturbance by potential predators, but when undisturbed, they protrude slightly.

If two colonies of Acropora touch in the Aquarium, there will very quickly be a winner and a loser.

It is likely that both will receive some damage where their flesh recedes to expose the white skeleton underneath, but one will cause the other to recede more.

Because of this, they are categorized as being aggressive.

The challenge of keeping Acropora is tied to their high demands for lighting, water flow, and pristine water chemistry.

The challenge is compounded by their need for incredible Stability of those Parameters. On the surface it sounds simple but those that have successfully kept Acropora understand the underlying difficulty.

If your tank is too large, it can be difficult for certain types of Corals to get the proper amount of light, so it’s a good rule of thumb to not have an aquarium any deeper than 24 inches for Coral Reef Tanks.

It’s also crucial for your Acropora’s health that, when first introduced to their new home, their depth is equal or close to that of their original tank.

Lighting Requirement

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 derives nutrients off of the byproducts of the dinoflagellates’ Photosynthetic Process. 

Zooxanthellae can provide what your Corals need to be able to grow and reproduce when they receive enough sunlight (and light in general) and other Nutrients.

These Photosynthetic organisms live in all sorts of different types of Corals, and they play a big part in every Reef Tank.

When your Acropora is getting too little light, the Zooxanthellae, which is typically brown, will begin to seek out more nutrients and build up on the surface of your Corals, giving it its brown Color.

But when your Corals are receiving too much light, your Acropora will begin to expel Zooxanthellae, which results in your Acropora becoming more and more pale until it looks bleached.

Most Acropora will do just fine with 200 to 300 PAR, but with a few specific types of Acropora, they can take up to 750 PAR.

Just remember to check the needs of your specific coral before adjusting anything.

If you’re unsure about the required amount of PAR for your Acropora and want to make sure they’re getting everything they need, there is one sure-fire way to tell: their Coloring.

If your corals are receiving enough PAR, you’ll observe healthy growth and vibrant coloring.

But on the other hand, if they’re not receiving enough light, they’ll begin to turn dark or brown .

Water Flow

As with any Coral, water flow is needed to deliver nutrients to corals while also removing waste and preventing algae and other microorganisms from settling.

As mentioned before, these Corals live on the top of Reefs where water flow is naturally high due to wave activity.

Not only do Acropora need high Water Flow but they also need random Water Flow. Random Water Flow from an Aquarium wavemaker will ensure that the Coral grows naturally, higher flow can result in thicker branches while lower flow will cause the Coral to expand as much as possible.

As the Coral Grows, the Overall Flow throughout the Colony will naturally decrease. This can cut off Nutrient exchange from the densest areas of the Colony and even start to impede delivery to nearby Colonies.

The answer to this is simple: add more flow or frag the colony to increase water movement once again.

Always keep an eye on how efficiently water is circulating throughout the System to Maintain steady growth.

Water Parameters

Acropora respond very poorly to sweeping changes in chemistry.

There are three major chemical parameters that are needed by Acropora to build its stony skeleton.

These are Calcium, Alkalinity, and Magnesium.

These chemicals help them build their stony skeleton.

Here are some quick stats about the ideal water chemistry for

Acropora Coral care:

• Hardness: 7,7-9 dkH
• Calcium: 400-450 ppm
• pH: 8.1-8.4
• Salinity: 35 g/L
• Nitrates : 2 and 10 ppm
• Phosphates: 0,03-0,2
• Magnesium: 1200 - 1400
• Strontium: 8 - 10
• Temperature: 73° - 78° F
• Salinity / Specific Gravity: 1.024 - 1.026

Diet / Nutrition

For the most part, Acropora Corals get the food they need through their symbiotic relationship with photosynthetic Dinoflagellates called Zooxanthellae.

These Stony Corals do not respond well to target feeding.

Most times, they will retract their Polyps and start to excrete slime and filaments to protect themselves.

On the other hand, they have successfully been broadcast fed a variety of dedicated coral foods as well as Zooplankton and small organisms.

Small Zooplankton include things such as rotifers and Cyclops Plankton. The rotifers we feed are usually around 0.5mm in size.

Cyclops Plankton are larger typically between 1-2mm.

They come frozen and are basically a small granular oily paste that creates an orange cloud when introduced into the tank.

The presence of rotifers in the water is immediately apparent to the corals because many of them will immediately open up and start their feeding behavior.

Acropora do this to a lesser degree but what is noticeable are white strings of mucus leading to each of the small polyps.

Over the next several minutes, the Acropora Corals will retract the strings and feed on the Zooplankton trapped.

The polyps typically extend further at night to help capture Plankton and organic matter from the water.

Some hobbyists like to give their SPS Corals Amino Acids .

These Supplements chemically help with protein production which can lead to increased growth and more vibrant Colors.

Fragging / Propagating

Captive propagation of Acropora is widespread in the reef-keeping community.

In a well-maintained Reef Aquarium, finger-sized fragments can grow into medicine Ball-Sized Colonies in one to two years.

Fragging these corals is not difficult, though it can be intimidating to work with a very expensive or sensitive species.

If you’ve ever fragged any other kind of branching SPS coral before, the method is the same. You can choose more desirable tips from the colony, not just a straight stick . It is also important to take from a place on the Coral where the natural contour of the Colony isn’t lost or impeded.

Pests / Diseases

If your Coral isn’t experiencing bleaching but still losing flesh, then there might be a deeper underlying problem like disease, infection, or pests.

Slow tissue necrosis (STN) and rapid tissue necrosis (RTN) are somewhat of a mystery in the Aquarium Hobby. These conditions cause the Coral to lose its flesh gradually or all at once with no apparent reason; this can happen overnight to an Aquarium that has successfully been running for years.

Right now, it is believed that these conditions are caused by an unknown organism that causes an unfavorable reaction due to changes in environmental conditions.

There is no known cure for STN or RTN either, though recovery attempts can be made through quickly fragging the coral or dipping the Coral in an Iodine solution.

Acropora sometimes fall victim to a variety of pests.

The two most commonly seen in home Aquariums are Acropora eating Flatworms and small crustaceans hobbyists call “Red Bugs.”

Acropora eating Flat Worms are extremely difficult to see.

This is due to their bodies mimicking the color and texture of the Coral itself.

The only tell tale sign of them is the Acropora will lose its brilliant color for a more tannish brown appearance and show white bite marks.

The coloration of the Acropora alone is easy to dismiss.

As we have discussed before, Acropora can change color dramatically for numerous reasons so often times a hobbyist will ignore a colony starting to brown out and attribute the change to some other changing parameter.

Once the white bite marks start to appear though it is clear that there are Flatworms present and the Coral must be treated with a series of Pest Control Dips to remove the existing Flatworms as well as newly hatched Flatworms that emerge from the eggs that are resistant to dipping.

In some extreme cases of Flatworm infestation, the Pest Control Dip will dislodge a shocking number of Flatworms to the point that it looks like there were more Flatworms on the Coral than actual Coral flesh.

Luckily, there are a few products available to treat Acropora-Eating Flatworms, though these treatments are aggressive and will need regular water changes to ensure that other Corals stay safe.

There are a few Livestock options for Pest Control too, like Halichoeres species of Wrasse along with Leopard Wrasses (Macropharyngodon Meleagris), though this is not guaranteed.

Red Bugs are less of a concern than Flatworms but should be removed none the less. They are essentially fleas on the coral that irritate the colony and might slow the overall growth of the Coral or limit its coloration.

The issue with Red Bugs is that they are very small and are difficult to see. Most hobbyists with Acropora struggling with red bugs never even know the pest is present.

The best prevention method is to dip all of you Coral, especially Acros, in Coral RX Coral Dip before adding them to your Reef Tank.

Additionally, Quarantining the Corals before adding them to your reef to ensure there are no pests will help prevent Acropora Red Bugs.