When corals start to grow in a confined area such as a reef tank, life can start to become crowded. While some corals can touch, others can’t, often resulting in chemical warfare.
In the wild, corals naturally grow over each other, Acropora (Acros) being one of them. If you have ever been snorkeling or diving on shallow reefs in the Indo-Pacific, you will see how Acropora can coexist with other SPS corals, but what you will notice, is how Acropora usually dominate these areas. This is because Acropora corals do not consider personal space. After all, their role is to constantly grow to survive.
When adding any corals into your aquarium, particularly LPS (large polyp stony) and SPS (small polyp stony) corals such as Torches and Acropora, it is recommended to place them in an open space where they cannot touch each other. But what if the same species were to grow too close to each other, or accidentally touch, is it something you should be worried about?
Can Acropora Corals Touch Each Other?
Many corals are known to be aggressive, and sometimes different corals will attack their neighbors by stinging them to survive or to outcompete for space. Some, however, don’t mind having a neighbor, which is typically true if you place two of the same species of coral together.
Acropora corals are known as the “crown jewels” of aquariums, and while they may not look dangerous, they are known to be aggressive coral. Now, they may not have sweeper tentacles teamed with “deadly” stinging cells (scientifically known as nematocysts) or join in on mass chemical warfare, but Acropora corals do have a powerful sting should any corals (including other Acroporas) get too close.
Branching Acropora corals contain mesenterial filaments; white stringy material that is used for feeding and fighting. The mesenterial filaments contain specialized stinging cells, which is what provides them with their powerful sting. As already mentioned, some corals will live in harmony, therefore, they will not resort to using their mesenterial filaments as a defense mechanism.
Corals grow by branching or encrusting, and once they start, they have no off button. This means that anything or anyone that gets in the way of your Acropora corals may touch. When two Acropora corals touch, the winner and loser of the match is determined rather quickly! So, even if you have two compatible Acropora corals, it is always best to avoid them touching, if possible.
If you are worried about your Acropora corals getting too close, monitor their temperament and move them to a more suitable area, just in case one experiences some serious damage. However, the rule of thumb usually is if you keep the same species of SPS corals near each other, they should be fine to touch without harming one another.
The two species of Acropora that are known to be the most aggressive are Acropora hyacinthus and Acropora palifera.
What Happens When Acropora Corals Touch Each Other?
When corals decide to touch, it can be very unpredictable what will happen next. Sometimes, one Acro will win and continue to dominate the other one either by branching or encrusting over it, but, occasionally neither Acro will take serious damage if they touch each other.
In the wild, corals have to naturally fight it out, as no one can come along and move one out of the way of the firing line. Some aquarium hobbyists do the same, allowing nature to take its course, but many others will intervene, given the circumstances.
Once two aggressive Acros start, it can be difficult to control after the “coral battle” is in full swing! Some Acros will battle it out to a stalemate, while other Acros don’t give up, and will continue to fight until the other coral has taken significant damage, or has been killed.
After a while, other branches in the Acro colony may get involved to fight for space. At this point, you can start fragging/trimming the parts that are starting to touch or have already experienced some damage.
There are a few things you may notice during or after an Acropora coral battle:
- Acropora sometimes displays brown spots from elevated stress levels.
- Your Acros polyps may not open due to the stressful conditions of an unwelcome neighbor.
- Your Acropora may start to turn white – the damage from fighting can lead to tissue necrosis. This is where the tissue is stripped, and the skeleton is left exposed.
- Your Acropora could start turning brown at the tips. When Acros are recovering from damage, a higher concentration of zooxanthellae is present as the polyp starts regenerating tissue.
Tips To Preventing An Acro Battle!
- Position corals away from aggressive neighbors.
- Allow plenty of space between corals.
- Perform regular water changes to remove any chemical warfare.
- Trim back any corals that get too close. The frags can be placed somewhere else in your aquarium to grow another coral colony.
Corals are animals, not plants, therefore, just like humans, they also have different personalities. While some Acros are friendly to others, some prefer plenty of personal space!
Just remember, when deciding where to place your Acro, think ahead and give them enough space to fully establish, and before they get the chance to touch, you should trim or frag your Acro coral if you want to avoid any aquarium conflict.