Is There A Dominance Hierarchy Amongst Corals? A Complete Guide

If you have ever looked at your reef tank and wondered why a once-thriving Acropora is suddenly losing tissue on one side, you are not alone. Many hobbyists start their journey thinking of corals as peaceful, colorful plants, but the reality is much more intense.

In the wild and in our home aquariums, corals are actually highly competitive animals that engage in constant battles for space and light. You might be asking yourself, is there a dominance hierarchy amongst corals that dictates who wins these silent wars?

The short answer is yes, and understanding this hierarchy is the secret to a long-term, successful reef tank. In this guide, I will walk you through the fascinating world of coral aggression, help you identify the “bullies” of the reef, and show you exactly how to place your corals for a peaceful, thriving ecosystem.

Understanding the Silent War: Is There a Dominance Hierarchy Amongst Corals?

When we talk about whether is there a dominance hierarchy amongst corals, we are looking at how different species interact when their personal space is invaded. Unlike fish, which can swim away from a fight, corals are sessile organisms, meaning they are stuck in one spot.

Because they cannot move, they have evolved a sophisticated arsenal of biological weapons to defend their territory and expand their reach. This creates a natural pecking order where certain species almost always “win” a physical encounter with another.

In my years of reef keeping, I have seen a small, unassuming Galaxea coral take down a massive colony of Montipora overnight simply because it had a higher “rank” in the chemical and physical hierarchy. Understanding these ranks is crucial for any hobbyist.

The Basis of Coral Competition

The hierarchy isn’t just about being “mean.” It is a survival strategy. In the ocean, space on the reef is the most valuable real estate on the planet. Corals fight for two primary resources: light and nutrients.

If a faster-growing coral shades a slower-growing one, the slower one will eventually die. To prevent this, the slower-growing coral might develop long-range stinging tentacles to “clear a path” and keep the neighbors at bay.

This dynamic creates a complex web of interactions where Large Polyp Stony (LPS) corals often dominate Small Polyp Stony (SPS) corals through physical stings, while Soft Corals often use chemical warfare to stunt the growth of their neighbors.

The Weapons of Reef Warfare

To understand the hierarchy, you first need to know how these animals fight. Corals don’t have claws or teeth, but their methods are arguably much more effective. They use three primary methods to assert dominance.

Nematocysts and Sweeper Tentacles

Many LPS corals, such as Euphyllia (Torches, Hammers, and Frogspawn), possess specialized stinging cells called nematocysts. When the lights go out, these corals often extend “sweeper tentacles” that are much longer and more potent than their daytime tentacles.

I have seen Torch corals extend sweepers up to six inches in a strong current! These sweepers drift in the water column and sting any neighboring coral they touch, causing localized tissue necrosis or even total colony death.

Mesenterial Filaments

This is perhaps the most “alien” way corals fight. Some corals can actually extrude their stomach linings—known as mesenterial filaments—onto a neighboring coral. These filaments contain digestive enzymes that literally eat the living tissue of the rival coral.

Favia and Chalice corals are notorious for this. If you place a beautiful Acan too close to a Chalice, you might wake up to find the Acan has been partially digested. It’s a brutal reminder that is there a dominance hierarchy amongst corals that we must respect.

Allelopathy (Chemical Warfare)

Soft corals, like Leathers (Sarcophyton) and Sinularia, often lack the stinging power of LPS corals. Instead, they use allelopathy. They release toxic chemical compounds into the water that inhibit the growth of other corals, particularly SPS.

If you’ve ever noticed your Acropora looking “grumpy” or refusing to extend polyps when a large Leather coral is nearby, you are likely witnessing chemical warfare. This is why active carbon is a reef keeper’s best friend in a mixed reef tank.

Ranking the Aggressors: Who Sits at the Top?

While every tank environment is different, we can generally rank corals into a hierarchy based on their aggression levels. Knowing where your new purchase sits on this list will save you a lot of heartache.

The Apex Predators (High Aggression)

At the top of the is there a dominance hierarchy amongst corals are the “tank killers.” These species require significant “social distancing” from all other corals.

• Galaxea Corals: Known as the “Galaxy Coral,” these are arguably the most aggressive corals in the hobby. Their sweepers are incredibly long and their sting is exceptionally powerful.
• Hydnophora: Often called the “Horn Coral,” these are unique because they will often win a fight even against other aggressive corals. They use mesenterial filaments to digest anything they touch.
• Bubble Corals (Plerogyra): Don’t let their soft, grape-like appearance fool you. They have potent sweepers that can deal massive damage.

The Enforcers (Moderate to High Aggression)

These corals are manageable but need careful placement. They will usually win a fight against most “peaceful” corals.

• Euphyllia Species: Torches are the most aggressive of this group, followed by Hammers and Frogspawn. Interestingly, Hammers and Frogspawn can usually touch each other without fighting, but a Torch will often sting both!
• Chalice Corals: They look like flat, colorful plates, but they are masters of night-time chemical and physical attacks.
• Acanthophyllia and Scolymia: These large fleshy corals have a powerful sting to protect their immediate perimeter.

The Passive Growers (Low Aggression/Vulnerable)

These corals usually lose the physical fight. They rely on fast growth or chemical defenses rather than stinging power.

• Acropora and Montipora (SPS): These are the “gentle giants” of the reef. While they can grow over other corals to shade them out, they almost always lose a stinging match.
• Zoanthids and Palythoas: These can be invasive and grow over other corals, but they rarely “attack” at a distance. (Note: Some Palythoas are highly toxic to humans, so handle with care!)
• Leather Corals: As mentioned, they use chemicals rather than stings. In a physical “touch” test, they usually lose to LPS.

Practical Placement Tips: Avoiding the “Sting Zone”

Now that we have established that is there a dominance hierarchy amongst corals, how do we use this knowledge to build a better tank? As an experienced reefer, I follow a few “golden rules” for placement.

1. The “Two-Inch Rule” (Minimum): For most corals, you want at least 2-3 inches of space between them. For aggressive LPS like Torches, I recommend 6 inches or more of clearance in the direction of the flow.

2. Consider the Flow: Remember that sweeper tentacles and chemical toxins travel with the current. Never place a highly aggressive coral directly “upstream” from a sensitive, expensive SPS colony.

3. Use the “Rock Island” Method: For corals that grow quickly and can be aggressive (like Green Star Polyps or Xenia), place them on a separate rock island on the sand bed. This prevents them from climbing onto your main rockwork and smothering your other corals.

4. Monitor at Night: Use a red-light flashlight to check your tank an hour after the lights go out. This is when you will see the true extent of the sweeper tentacles. If you see a sweeper touching a neighbor, it’s time to move one of them!

Managing a Mixed Reef: Peace Through Chemistry

If you want to keep a “mixed reef” (a tank with SPS, LPS, and Softies), you are essentially managing a multi-species war zone. But don’t worry—this is completely doable with the right maintenance routine.

Since is there a dominance hierarchy amongst corals that includes chemical warfare, you must manage the water quality to neutralize these “invisible” weapons. Running high-quality activated carbon is the best way to do this. I recommend changing your carbon every 2-4 weeks to ensure it is effectively pulling out the terpenes and toxins released by soft corals.

Additionally, regular water changes help dilute the chemical signals corals use to stunt each other’s growth. Think of it as clearing the air after a heated argument. It gives the less dominant corals a chance to breathe and grow.

Signs Your Corals Are Fighting

Sometimes, we don’t catch the fight in action. You need to be a “reef detective” to spot the aftermath of a hierarchy dispute. Look for these signs:

• Localized Tissue Loss: If a coral is white or “bleached” only on the side facing a neighbor, it has likely been stung.
• Excessive Mucus Production: Corals often produce a thick slime coat when they are stressed or being attacked chemically.
• Mesenterial Filaments Visible: If you see white, stringy “guts” coming out of a coral’s mouth or side, it is actively attacking or defending itself.
• Retraction: If a coral stays closed for several days while its neighbors look fine, it might be losing a chemical battle.

Pro Tip: If you see a coral being stung, move it immediately. However, do not place it in a high-flow area right away, as the damaged tissue is fragile and can easily blow off, leading to “Brown Jelly Disease.”

FAQ: Is there a dominance hierarchy amongst corals?

Which coral is the most aggressive?

In most home aquariums, the Galaxea coral is considered the most aggressive due to its exceptionally long and potent sweeper tentacles. Hydnophora is also a top contender because it can digest other corals upon contact.

Can different species of Euphyllia touch each other?

Generally, Hammers (E. paraancora) and Frogspawns (E. divisa) can touch each other without issue. However, Torch corals (E. glabrescens) are much more aggressive and will often sting Hammers or Frogspawns if they come into contact.

Do corals of the same species fight?

Usually, no. Most corals of the same species (conspecifics) can touch each other safely. For example, you can plant a “garden” of different colored Zoanthids or different types of Acropora close together, and they will simply grow around each other.

How can I stop my leather coral from killing my SPS?

The best way is to use activated carbon in a reactor or a high-flow area of your sump. This absorbs the toxins (terpenes) released by the leather coral. Ensuring good water turnover and regular water changes also helps significantly.

Can corals “sense” their neighbors?

Yes! Studies have shown that corals can detect the chemical signatures of nearby rivals. Some corals will actually redirect their growth energy into developing more “warrior” polyps (sweepers) when they sense a competitor nearby.

Conclusion

So, is there a dominance hierarchy amongst corals? Absolutely. The reef is not just a collection of pretty colors; it is a dynamic, competitive environment where every organism is fighting for its place in the sun.

Understanding this hierarchy is what separates a beginner from a successful long-term reef keeper. By recognizing the weapons each coral uses—whether it’s the long reach of a Torch coral’s sweepers or the invisible chemical cloud of a Toadstool Leather—you can design a tank that minimizes conflict.

Remember to observe your tank at night, provide ample space between different groups, and use chemical filtration to keep the peace. With these tools in your belt, you can create a stunning, harmonious underwater world where every inhabitant has the room it needs to thrive.

Happy reefing, and may your sweepers stay short and your polyps stay extended!