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Acropora is the most numerous family of the SPS coral group. No other genus has such a large number of genera as Acropora. In terms of maintenance, it is one of the most difficult corals. So why is it so popular in marine aquaristics?

To start with, a little history…

Acropora is a genus of hard corals with relatively small polyps. Acropora originates from the subclass Zoantharia and the order Scleractinia. The family Acroporidae was defined by Verrill in 1902. Acropora corals are the most abundant corals and contribute the most to coral reef formations worldwide. To date, 150 different genera of Acropora have been described.

Acropora in the wild

Acropora inhabit most of the world’s reefs. The area of occurrence is the Indo-Pacific, Great Barrier Reefs, Fiji, Tonga, Solomon Islands. They live on the slopes of the upper reefs where there are very strong currents. Some species are also found in deep water, lagoons and muddy waters.

Acropora

Description 

The coral forms colonies that take different shapes, such as branched or flatter forms.

The shape of the Acropora depends on where it is found in the ocean. In turbid water, corals will be very thick, while the same species may be long and thin in deeper waters with less water flow. The analogy is the same in an aquarium. The same coral placed in different locations looks different.

Acroporas have very porous and lightweight skeletal structures. Small polyps protrude from their branches. The coral lives in symbiosis with Zoxanthellae, which provide the coral with the necessary energy for life.

 

acropora 2

Requirements

Acroporas are not among the easiest corals to maintain. The difficulty of this species is that the corals need stable conditions to live in and do not like change, so they are hard to forgive mistakes by aquarists. They are particularly sensitive to fluctuations in KH and PO4.

 

Acropora 3

Care of the coral in the aquarium

Parameters

It’s worth paying attention to the basic and extended parameters. Out of respect for the readers, we will only refer to a few of them. For more on the extended parameters, see the article on ICP parameters.

Basic and main parameters for acroporas:

  • KH – carbonate hardness, which, depending on how you want to keep, can be 7-12 dkh. I personally keep Acroporas at a Kh of around 8 dkh.
  • Ca – calcium, which can be kept in the range of 400-440 ppm. I personally recommend a level of 440 ppm.
  • Mg – magnesium, I recommend keeping at a level of 1250-1450 ppm. I personally keep a level of 1350 ppm.

All 3 parameters are needed by acropores to build up their calcium skeletons. Acropores are particularly sensitive to fluctuations in Kh. They accept a maximum difference of 0.7 dkh per day. It is most important that calcium and magnesium remain within the correct range. Acroporas tolerate calcium and magnesium changes better. From my observations, a rapid upward change in Kh is almost imperceptible to Acroporas, whereas a decrease stresses them a lot and can even cause the death of the coral.

  • PO4 – low but not zero levels are required. I personally keep PO4 in the range of 0.04-0.08, but a safer level is 0.08 ppm. Phosphate levels will in Acropora affect the thickness of their tissue and the brightness of their colour. Tissue thickness in coral will largely depend on the aquarist’s level of expertise in aquarium management.  The thicker the tissue, the deeper the coral will be slightly darker, but also more resistant to change. At the beginning of the adventure with Acroporas, it is better and safer to maintain a slightly higher PO4 level, e.g. 0.1. Acroporas do not like rapid PO4 changes, especially upwards, so a constant phosphate level should be provided.
  • NO3 – the recommended level is 0.5 ppm, but I have seen beautiful aquaria with NO3 20, so you can see that Acroporas tolerate NO3 ranges.
  • pH – 8.1-8.4 – not only do you need to ensure that the pH level is appropriate, but also that it is stable. It is worth reading the article on the importance of pH in the marine aquarium, in which I described the effects of pH on coral health. For Akropor, pH is very important, so it is worth taking care of it.
  • A constant temperature of 24-27 °C / 75-80°F;care should be taken to ensure that the temperature is not only within the norm, but also that there are no rapid fluctuations.
  • Salinity 33-35 ppt. At this point we also take care to keep the salinity constant. If we decide to take a salinity of 33 ppt, we stay at this level. Any change in salinity will cause all parameters to change.

Extended parameters

This is where the ICP OES water test, which examines 40 different elements, comes to our aid. It is worth performing these regularly, not only to check that our dosing method is well configured, but also to check for contaminants or exceedances. Contamination in the form of heavy metals is a very common problem. The most common contaminants are pump impellers or metal components within the water, which corrode and release rust into the water.

The main minerals in this group include potassium, strontium, iodine, sulphur or zinc. These are very important components for coral health.

Lighting

The Acropora coral has specific requirements for feeding it with light. The coral lives in a symbiosis with the algae zoohanthellae. These algae are photosynthetic organisms, while the coral derives nutrients from the by-products of the photosynthetic process of the symbiotic algae. Zooxanthellae is usually brown in colour and the coral manages its population, with which it lives in symbiosis. Too little light will cause the coral to turn brown. This is because the coral will seek more nutrients. More zoxanthellae means more energy. If the Acropora has more light, it gets rid of the zooxanthellae, the colour of the coral becomes brighter. The right amount of light is needed for the health of the coral, and you cannot overdo it one way or the other, so when choosing a lamp and setting the power, it is a good idea to measure the light level with a PAR meter.

 

Acropora 4
 

Any experienced aquarist will agree that Acropora is a coral that really loves light. According to our observations, Acropora does best with a PAR of 300-500, but keep in mind that every aquarium is different and good quality light even with a slightly lower PAR will do the job.

I think it is worth adding at this point that new corals that we have just bought, especially those that have not had the right amount of light, should be placed lower at the beginning, where there is less PAR, and gradually raise it upwards. This will cause the coral to gradually adapt to the new conditions. If you are inserting more corals or changing to a higher-powered lamp, it may be a good practice to use the acclimation function of the lamp. This allows a gradual transition from lower to higher wattage. The corals will adapt to the lamp power and grow healthier.

Circulation

Acropora are found in strong currents in reef areas. Corals of the Acropora species benefit quite a lot from strong water movement in the aquarium. On the one hand, stronger water movement provides the coral with more nutrients, on the other hand, it removes unwanted compounds from the coral.

The Acropora grows much denser in areas with stronger circulation. The growth of coral branches is also important to maximise the growth of bacteria between their stems. According to scientific studies, the lower the concentration of bacteria around a coral, the less dissolved substances in its internal space. It may be interesting to note that corals grow in such a way as to maximise the bacterial culture around them.

When it comes to planning the circulation for the Acropora, the fact that the colony will grow must also be taken into account. A large colony reduces the water circulation considerably. They can even reduce the water circulation inside themselves, so the circulation in the aquarium should be improved from time to time. Corals grow and need better circulation for further development.

Feeding

The first element I wrote about in the context of feeding is the coral’s relationship with the symbiotic Zooxanthellae. Good quality light in the tank provides the coral with energy. The Zooxanthellae, by performing photosynthesis, provide energy to the coral.

In order to enjoy beautifully growing corals, I recommend using amino acids, which are the building blocks of the cell, have a protein-building role, and are responsible for neurotransmitter transport and biosynthesis.

Another excellent food for corals is small zooplankton (rotifers 0.5 mm and plankton 1-2 mm), also in frozen form. After feeding, we can notice that the coral pulls out polyps and even mucus. In doing so, it picks up zooplankton.

The right number of fish will provide the coral with adequate levels of NO3 and PO4, which is also consumed by the symbiotic algae and converted into energy for the corals at a later stage.

Aggression – where to place acroporas in the tank

Acropores between different subspecies can fight each other. When placing corals in an aquarium, we must anticipate their growth rate and provide enough space for them to grow freely. Corals have relatively short polyps, so they are unable to reach other corals that are more than a few centimetres away from them.

Diseases and problems

In some situations, Acropora can be affected by Rapid Tissue Necrosis (RTN) or Slow Tissue Necrosis (STN). There are various theories for the occurrence of this phenomenon. Some of them speak of fluctuations in parameters, but in many cases RTN or STN have occurred in tanks that had constant parameters. Other known theories are bacterial infections,and it is this theory that appeals to me, especially as I have heard several times from experienced aquarists that dipped the coral when STN/RTN occurred, and it had a positive effect. Alternatively, you can break off a piece of coral where there is still tissue and stick it to the rock. The coral will grow back.

Another enemy of Acropora are flatworms, flat transparent worms that attach themselves to the coral and lay eggs on it. Once the problem has been diagnosed, we need to have the coral dipped. If the corals are too large and the problem affects the entire tank, the entire aquarium must be treated with the appropriate preparations. This will cause many animal problems, including putting the fish at risk of death. This is because the dying flatworms give off toxins into the water. With this solution, it is necessary to do water changes and to change the carbon frequently enough. This is not the subject of this article. When embarking on treatment in this way, it is important to prepare thoroughly.

Red bugs are very tiny. They run over the coral and irritate its tissue. The coral is stressed by the bugs and grows more slowly. Regular dip products do not help against these worms. More aggressive products to kill the insects are effective. The best product for these worms is Interceptor.

The best method is to properly dip the corals before putting them in the tank. It is better to prevent the problem than to treat it later.

Varieties most commonly kept in the aquarium:

  • Acropora tenuis
  • Acropora millepora
  • Acropora valida
  • Acropora microlados
  • Acropora florida
  • Acropora formosa
  • Acropora humilis
  • Acropora hyacinthus
  • Acropora microphthalma
  • Acropora nasuta
  • Acropora carduus
  • Acropora echinata
  • Acropora anthocercis
  • Acropora verweyi
  • Acropora valida
  • Acropora yongei

Summary

In the article I have introduced the subject of Acropora. They are extremely beautiful when we take care of them. In stable tanks they form multicoloured colonies. There is probably nothing more beautiful than polypoid Acropora in wonderful colours. They convinced me and. I am currently creating a new Acropora tank.

About the author

Picture of Marek Protasewicz

Marek Protasewicz

Reefkeeping has been my passion for over 10 years now. I love learning. The hobby has taught me many valuable lessons, patience being the best example. Combining work and passion is my path. I run Crazy Coral, a marine aquarium shop, for a number of years. Building this business from the scratch I learnt from my own mistakes at a heavy cost.
Later I managed a project aimed at development of methods for quick growth of Corals in non-natural conditions. The project was carried out by Get Sales, Poland. Presently, I am responsible for distribution strategy at Reef Factory, of which I am a co-founder. The company produces smart devices for marine aquaristics. The last projects I have been involved in are Social Reef and ReefPedia.

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