To get healthy specimens quickly

Have you ever noticed a small frag from acropora surpassing in size the original colony in a few months? Have you ever noticed any acropora grow from a small crack where you dropped a frag the last time you used your cutting pliers? Why when you break an acropora's branch it will soon emerge a bunch of new small branches where there was only one?

Acropora are very primitive corals, with unique reproduction and survival strategies that have placed them at the top of hermatypic corals (reef constructors), in both quantity and diversity aspects.

Discover in this article some of the most effective techniques to speed up acropora propagation in captivity, with simple tricks and tips that you can use without having to invest in equipment or products of any kind. You will get healthy and beautiful specimens in a short time.

The critical size, a smart evolutionary improvement

As it is well known, acropora like many corals lack the ability to move, they are exposed to the threat of many predators who find in them the perfect meal. Consider for a moment what a coral is: fresh and nutritious meat that can not run away before the attack of any hungry predator, crown of thorns starfish, crabs, nudibranchs, butterfly fish and especially parrot fish.

A school of parrot fish formed by dozens of individuals with an average weight of 30 kgs can devastate a coral reef within a few minutes; this likeable animal is the main responsible for the formation of some of the coralline sand beaches that we like to visit. With their powerful beak they are capable of shredding several tons of stony coral in a few hours and engulf the fleshy tissue. But, just a moment…this can have a benefit for corals though it may seem unbelievable. When the school of parrot fish “flies over” the reef, they keep fragmenting and grinding branches of acropora (and other stony corals in lesser extent), many of them fall on the substrate; well, acropora have managed to turn their weakness into strength evolving to produce new colonies from small fragments of the original coral, which merge and embed on the bedrock. Thus a colony of old and sick acropora can be renewed and grow from scratch with the small fragments that have not been consumed.

acropora loripes

Scientific studies developed by GARF have proven that each acropora species has a critical size to embed and grow quickly. If the fragment is too small and the number of polyps scarce, it might not prosper, whereas if it is too large, the acropora branch “won't have noticed” that it has been fragmented and will continue to grow at a similar rate as it did before being attacked.

On the other hand, if the fragment has the critical size, an accelerated growth mechanism is triggered. It is as if the acropora would take awareness of its plight and devoted all its energy to embed and grow as quickly as possible to ensure its survival (remember that a coral is in constant competition with its neighbors for exposing its polyps to sunlight).

The critical size for acropora propagation is usually between two and three centimeters in most species. In table-like acropora it is always shorter than the length of the branch when it acquires vertical orientation.

Frag's tilt, yes, it matters

This is one of the conclusions that can be easily reached when propagating acropora. I remember what happened to me with some frags of acropora valida given to me by a good friend several years ago: as we usually do, I sticked several branches of different lengths onto a rock, vertically. One of these fragments broke off the rock and got encased in a horizontal crack: within a few weeks it embedded a base of several square centimeters and sprouted several vertical tips; and after a year I had a nice colony of acropora valida several times bigger than the other branches that I had sticked vertically onto the rock.

reproducción de acroporas

I might be related to the evolutionary adaptation mentioned at the beginning of this article: when an acropora fragment is broken by the beak of a parrot fish and lucky not scrunched in its mouth, it will fall onto the ground in a horizontal position in almost all occasions.

The most successful acropora are those which have developed this ability to embed quickly from small fragments “lying”.

This is particularly true for tree-shaped species (such as acropora valida from the example) and those that grow in a staghorn-shaped colony, also called stag.

It is just test and see which is the direction that most benefits the growth rate of the new colony of polyps; I have witnessed that in some cases you get good results by placing them lying with a small tilt, exposing the cutting to the sunlight.

Best accompanied

This is something that I find really surprising: an acropora frag will always grow much faster if we let it sit near other frags of the same species.

The few who have witnessed acropora's propagation in an aquarium by releasing eggs and sperm (sexually) know that this only happens when many polyps concur in one place, namely, when we put many acropora of the same species together or we have very large colonies. And quite odd, since this mechanism never takes place in small colonies or few in number. And how does the polyp know that it can release its gametes into the water? It makes sense that they do not waste energy if the chances of reproduction are low (poor presence of neighbouring polyps). For me it is a mystery, I guess there is a chemical signal that gives them green light for the production of reproductive cells, but the truth is that I do not know how and have not found information about it.

acropora echinata

Similarly to an acropora producing eggs and sperm when it feels accompanied, it also increases the birth of axial polyps. And this means growth rate.

An acropora that produces few axial polyps and many radial polyps is a coral that grows slowly or even nothing. The axial polyp is responsible for growing branches, no new axial polyps no new branches.

And how do you know if an axial polyp is active and growing? It's simple: its color lightens, growing tips have a low concentration of zooxanthellae and a high concentration of photoresist pigments. At a glance we can know if an acropora grows actively and this is usual when we get many frags of the same species together in the same area. Odd, don't you think so?

Cut short

Unlike other SPSs, acropora often have difficulty growing tissue on the surface of their own skeleton after an injury occur, something that has always surprised me. Acropora tend to form a kind of lip in that area, leaving part of its skeleton visible and vulnerable to be attacked by parasites or hairy algae.

acropora hyacinthus

When preparing frags for acropora propagation, always make sure to cut on healthy tissue and if there is any dead part of skeleton you can not remove because of a difficult access for the cutting tool, cover it with some epoxy resin for the tissue to grow over and embed with some polyps.

It is important to keep this area clean in the first days, at least until the new tissue begins to grow on the glued bond.

Razmatazz, by Eric Gordon at ARK Reef

Another very important reason for cutting on the healthy tissue is that the majority of parasites, special mention to amakusaplana acroporae (AEFW), tend to lay eggs in the dead zone near the coral tissue. By covering this area with epoxi resin or, even better eliminating it much diminish the risks of these parasites transmission.

Better snapping instead of cutting

It is possibly related to what I said about parrot fish at the beginning of the article, and it is quite logical. It's as simple as that in nature clean cuts don't happen “perfectly”, but irregular bites that leave some unprotected polyps inside damaged walls and septa corallites.

acropora austera

Acropora have learned to develop more axial polyps in these areas, which grow several times faster than the radial polyps arising from a clean cut.

This explains that when aa acropora branch breaks in the aquarium, a bunch of branches show up where there was only one.

Smart evolution about acropora propagation.

I've read and heard so many times that for acropora propagation (and other corals in general) it is very important to use very sharp tool, producing a clean cut with no tears. Nothing more wrong than this and it is easy to prove: when irregular fragmentation occurs , similarly to that produced by a parrot fish biting an acropora, polyps that have survived seem to “understand” that their survival is threatened and use all their energy not only to repair the damaged tissue (as it would occur with a clean cut), but also to grow as fast as possible and therefore produce new axial polyps that will end up like a “bunch of branches” in the area where before there was a single one.

And which is the best way to break a branch to achieve a fast acropora propagation? With a stroke? no: they are very hard, you will only achieve it on very large specimens and won't break it where you want. With pliers? neither: you would only produce tears and injuries on the acropora's tissues. I use two methods depending on the thickness of the branch to break:

  • Thin branches: I nip the branch on the place where I want to fragment it by using only the tip of the cutting pliers. This makes the branch break in a slightly irregular way.
  • Thick branches: I make a small cut with a circular saw (obviously taking the piece out of the water) in the same way a lumberjack chops the trunk of a tree. Then I insert the tip of a screwdriver and lever until it breaks. Thus I get irregular fragments without any tears, a convenient and accurate way.

Each growing tip produces the same amount of polyps

So is: each acropora branch we cut will grow containing the same amount of polyps that the original one, except if we kill or harm any polyp (involuntary stroke, attack of a fish or invertebrate…).

What does this mean in practical terms?

acropora lokani

Quite simply, there comes a time when it makes little sense to let grow a branch in a breeding colony. The only thing that will happen is that it will keep on dividing (creating axial polyps) under the same geometry.

This is particularly noticeable in the table shaped acroporas, with all their branches growing to the same length and extending widthwise (branches sprout only horizontally and quickly bend over to get vertical).

It is on this type of acropora where we should most often fragment branches to keep it with an active and orderly growth. As soon a branch reaches its final length (which is determined by the genetic information of the species itself), we can already turn it into a new frag.

And the best piece of advice

For acropora propagation: balance and stability

  • Parameters: alkalinity fluctuations, salinity…really slow acropora's growth, You must procure stable and balanced parameters to grow them healthy and fast.
  • Nutrients: I never get tired telling, acropora in ultra low nutrient systems are very beautiful and even striking but they do not grow fast. If this is your goal, do not mind letting the nitrate level rise slightly, 0,5 mg/l is a very reasonable value and, although pastel colours are lost, colour is still very good and growth takes off.
reproducción de acropora
  • Lighting: We all know that it is important to provide a strong lighting with proper spectrum in which the predominant wavelengths are near the blue colour. But few people take into consideration that acropora need time to acclimate to such a strong light, especially if they are freshly made frags. If you do not respect the time to acclimatize the new frag, it is very likely that the tissues of the most exposed areas get burnt and slow down the growth of axial polyps: they have excessive light, why are they going to grow higher?.

In very extreme cases, associated to high alkalinity level, we will produce necrosis on the acropora's tips and even its death if not corrected in time.

On the other hand, you must bear in mind, and this is addressed to lovers of the super-power leds, every species of acropora supports a maximum light level, which if exceeded may result in “photoinhibition”.

Overpassing this level of lighting leads nowhere, and you can even slow down the growth of the coral. It is as if a person is illuminated with so much light to read a book that he ends up dazzled with the brightness of the paper and has to struggle to keep on reading.

I hope these tips will be useful. They are things you learn over the years, based on long time wetting hands, and probably will not find in any book.

I'm sure there are many other techniques and tricks of great value for acropora's propagation, so if you know any, do not hesitate to contribute. It will be for the benefit of all people and especially of coral reefs, threatened every day.