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Are you looking at those amazing SPS tanks and wonder how to care for those rare Acroporas? I got you covered today as I go over Acropora coral care. I’ll go over their origins, what they need to thrive, how to maintain stability in your reef tank, and how to frag for Acros!
If you are getting started in what I call the pinnacle of the reef tank hobby, you have landed in the right place. Let me guide you today on this difficult to keep, but very rewarding coral. Master this coral, and you will see how amazing this experience in the hobby can be. Let’s get started!
An Overview On Acropora Corals
|Scientific Name||Acropora spp.|
|Common Names||Largely referred to as Acropora; the common name will be assigned with specific species|
|Origin||Widely found throughout the Indo-Pacific, few species present in the Caribbean|
|Common Colors||Greens, yellows, blues, purples, reds, pinks, oranges, browns|
|Lighting||High (200+ PAR)|
|Tank Placement||Middle, Top|
|Temperature Range||76-82 degrees F|
|pH Range||8.0 – 8.4|
|Salinity||1.025 or 35 PPT|
|Alkalinity||8 – 12 dKH|
|Calcium Level||350 – 450 PPM|
|Magnesium Level||1250 – 1350 PPM|
Origins And Habitat
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.
With approximately 150 known species within the genus Acropora, only three occur outside of those regions far away in the Caribbean1. These species are the staghorn coral (Acropora cervicornis), elkhorn coral (Acropora palmata), and fused staghorn coral (Acropora prolifera).
All three Caribbean species play a major role in the reef ecosystem. They provide shelter for juvenile fish and invertebrates and house a plethora of microscopic life.
Similarly, Acropora from the Indo-Pacific are also responsible for creating the calcium carbonate backbone of many reef ecosystems. They grow at the tops of reefs where sunlight is abundant. Their hard skeletons have adapted to withstand the constant push and pull of the waves above.
However, these stony corals have not adapted to the destruction caused by fishing trawlers, ship anchors, or the effects of climate change. Acropora have sadly become the face of dying reefs with lifeless white branches and deserted marine structures.
What Do Acropora Look Like?
Acropora are very easy to tell apart from most other corals, but can easily be confused with other small polyp stony (SPS) corals. Given that there are many natural species of Acropora as well as modified varieties from the aquarium hobby, it can be difficult to know exactly what you’re looking at. In general, it’s best to know the appearance of Acropora and then narrow them down from there.
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.
Acropora–and many other SPS species–are referred to as ‘sticks’. This is not a misnomer as these corals really do look like a series of intertwined branches, even more so when you receive a single branch as a frag.
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.
Placement In The Aquarium
Acropora need to be placed where light and water flow allows. This is typically at the top and middle portions of the reef, though some extremely high-tech setups may allow for lower portions to be utilized.
As we will discuss, these corals need plenty of room to grow and will fight each other when placed too closely together. That, and they can also grow into very impressive structures as well!
Temperament In The Aquarium
Though Acropora might seem harmless as they don’t have any apparent sweeper tentacles, they are actually very aggressive. These stony corals are determined to preserve their spot on the reef and will eagerly damage other nearby coral species.
Are Acropora corals aggressive?
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.
Some hobbyists frag their corals to prevent this from happening while others allow them to adapt and change paths. One thing is for sure though, good placement in the first place will prevent many future problems down the line.
Acropora Coral Care And Maintenance
Acropora corals are difficult to keep. But just how difficult are they?
Needless to say, even the most experienced hobbyists have difficulty cultivating a healthy and sustaining SPS system. There are a few reasons why they’re so challenging, though. This mainly comes down to the type of lighting, the intensity of lighting, and the spectrum of lighting as well as the direction and intensity of water flow.
In addition, nutrients and water quality play a huge role in the color and growth of Acropora, though their needs are relatively straightforward on paper; it is almost necessary to have an automated dosing system or calcium reactor when dealing with large numbers and colonies of Acropora to ensure stability.
Is Acropora a hard coral?
Acropora species are revered as the most difficult corals to keep in the home aquarium. These corals are very temperamental and don’t adapt to change. Flow, lighting, and nutrients all need to be in ideal ranges for Acropora to thrive. Even then, they may not survive.
There are two things that might happen to an unhappy Acropora: 1) the coral changes colors, otherwise known as ‘browning out’, or 2) the coral dies over the course of a few days or weeks regardless.
One of the biggest achievements of having an SPS system is having a display of colors. Though some aquarists might have great coral growth, lacking color can be enough for disappointment.
This challenge, and the large payoff for displaying intricate reef structures and bold colors, make Acropora the holy grail that keeps hobbyists coming back.
In nature, Acropora are found at the very top of the reef. The aquarium hobby has made it possible to keep them from the middle and up, though a large amount of light is needed.
The conundrum with SPS corals is that the more they grow, the more they shade out the lower branches of themselves. This, in addition to them being light-loving already, can make having a large colony for a long time very difficult.
SPS corals are especially susceptible to browning out when they don’t receive enough light and bleaching when they receive too much and/or are moved between environments too quickly. The perfect colorations will be reached through trial and error of different lighting fixtures, intensities, and spectrums.
At the very least, most Acropora species need at least 200 PAR. However, they usually don’t start thriving until placed under 300-500 PAR, with some systems successfully running above 600 PAR. That is a ton of light that your coral needs to adapt to over time.
Over the past few decades, hobbyists have argued about which light fixtures are best for Acropora. There is no clear consensus and success has been found under each type, whether it be LEDs, T5 fluorescents, or metal halides. My personal opinion, is try a hybrid system like the Aquatic Life system.
How many hours of light does an Acropora need?
Besides intensity and spectrum, Acropora have the same photoperiod as other species, making them easy to keep alongside other SPS and large polyp stony (LPS) corals.
In general, about 7-9 hours are recommended for peak settings with a couple of hours for ramp up and down. Of course, this will vary with each system, though anything below or above this could cause algae or other problems.
Acropora 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.
Acropora Water Parameters
SPS water parameters are somewhat of an oxymoron. These corals love clean water but need high, stable levels of nutrients for growth. This makes it very difficult to regulate in a home aquarium setting, though modern technology through automatic dosers and smartphone applications has made balancing nutrients that much easier.
There are a few parameters that you need to keep a careful eye on like alkalinity, calcium, magnesium, nitrate, and phosphate.
Alkalinity, calcium, and magnesium all work together to facilitate the growth and color of Acropora. They are usually introduced into the system through natural seawater or through marine salt mix or other supplements; as we’ll discuss later, these parameters are the most commonly dosed once coral growth becomes exponential.
On the other hand, nitrate and phosphate can be introduced into the reef aquarium through waste from fish, invertebrates, and bacteria. These parameters need to be low, but available. Generally, reef tanks run under 40 ppm nitrate and under .01 ppm phosphate. An imbalance of these parameters can lead to algae and poor coral growth.
For reefers who achieve this level in the hobby, the usual issue is lack of nutrients, due to the high end nature of their equipment. Dosing nitrates and phosphates are not uncommon!
As corals grow, they take up nutrients. For average aquarists, these nutrients are reintroduced into the system by way of water changes, fish waste, and other natural processes in the aquarium. However, once Acropora start to grow, they can start to have high demands.
More specifically, you will need to balance alkalinity, calcium, and magnesium. These three parameters work together to create stability. Perform regular tests to observe which and how nutrients are being used throughout the system and add as needed. It will take time and testing to find which product combinations work best for your system.
For alkalinity, calcium, and magnesium especially, it is imperative to change parameters slowly. This is done over the course of weeks and months. However, once the deficit is realized, dosing can be done weekly or as needed by a scheduled application or machine. There are also auto tools like the Neptune Trident that can automate dosing entirely. A trident is something to consider if you are considering designer Acropora corals.
Sometimes, home aquarium systems can be too clean. In this case, phosphate and/or nitrate might need to be dosed. Though this can sometimes be fixed by feeding more heavily or even introducing new livestock into the tank.
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.
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.
Do Acropora corals grow fast?
For as difficult are Acropora species are, they are relatively fast growers. Of course, this doesn’t mean that your tank will be filled out with coral in the first few months of introducing them to your system, but over years, you will have a thriving ecosystem comparable to those in the wild.
It should be noted that it can take quite a while for some Acropora to settle in. They will likely turn brown over the first few weeks and months of introducing them into your aquarium. But they will quickly establish themselves and start to grow once stability has been reached.
What Are Good Tankmates For Acropora?
Acropora corals can be kept with all reef-safe species. In fact, Acropora do best when they receive natural nutrients from fish waste.
As these corals can grow very large and need intricate reef tank setups, most aquarists have as much space as they need to house a variety of fish species. Some of these options usually include tangs which can also be beneficial for picking away any algae that might start at the base and lower portions of the colonies.
It should be noted that some fish, like butterflyfish (Chaetodontidae family), are largely regarded as being not reef-safe. That being said, many hobbyists have found that they aren’t as likely to pick at SPS coral as they are at LPS or soft corals. Still, always use caution when adding a possibly not reef-safe species.
Fragging Acropora can be profitable and might be necessary over time as your corals start to grow. 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.
For a clean cut, an electric saw is recommended. Otherwise, you may use a bone cutter. Simply cut the piece of Acropora where desired and use a coral dip or iodine for better recovery. For the bone cutter method, see the video from C&M Aquatics below for a visual.
If selling these frags, you may want to pick the more desirable tips from the colony and 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.
Sometimes you might find that you’ve accidentally knocked off a piece from one of your colonies while doing maintenance in the tank. Simply stick this piece on a piece of rock or attach it to a frag plug. Chances are that it will make a full recovery and start forming its own colony!
Why is your Acropora turning white?
In most cases, your Acropora is turning white because it is not happy. Bleaching is when the coral expels the symbiotic zooxanthellae from its calcium carbonate skeleton, leaving the colony stripped of color. This is in response to unfavorable conditions or sudden changes in water chemistry.
For most hobbyists, it will be very easy to tell where the mistake was, especially if other corals in the tank bleached too. However, sometimes these things are untraceable and seemingly have no rhyme or reason. Once the coral has fully bleached, there is little to no chance that it will recover and algae will quickly cover the white remnants.
If only one area of the coral has started to bleach then there is some hope, though recovery will be difficult. All in all, the most important aspect of a reef tank is stability. The problem is that you need stability while also addressing the problem, which might require gradually changing parameters.
This needs to be a slow and steady process. The coral can absolutely recover, but it will take a few months.
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 & Rapid Tissue Necrosis (STN & RTN)
Both 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.
Many SPS corals have their own designated pest invertebrate and Acropora corals are no different. These flatworms are very difficult to see but can be reflected by the overall loss of color in the coral. Small missing pieces of flesh on the coral will also gradually spread across the colony, indicating where the flatworm has eaten.
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.
Acropora-eating flatworms can be very difficult to diagnose and even more difficult to treat. It is possible, though.
Where To Purchase Acropora Corals
Acropora Corals can be purchased from either local fish stores or online reef shops. When search for Acroporas, the reputation of the seller is critical and you should only work with a what you see is what you get (WYSIWYG) coral seller if looking online.
Acroporas are designer corals these days. There are many Acros with their own brand names now that are associated with the coral seller or store. Many fetch for high prices. Be prepared to shop around and look to be selective if you are start looking for designer corals.
Acropora are the end goal for many hobbyists: they have incredible colors and grow into immense structures. Sadly, the rumors are true and these corals are the most difficult to keep due to their need for high lighting, high water circulation, and stable water parameters.
Still, they remain a trademark for the picturesque home reef aquarium.