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Coral dominance hierarchy sounds complex, but it is simply the way corals decide who gets the best space, light, and flow on a reef. In the wild and in your aquarium, corals are not passive decorations. They fight, they defend, and they grow over each other. Understanding who usually wins, how they fight, and how to plan your tank around this behavior will save you coral loss, frustration, and money. This guide explains the rules of coral competition in simple terms, with clear examples and practical steps you can use in your home aquarium.
What Is a Coral Dominance Hierarchy?
A coral dominance hierarchy is the order of power among corals living close together. Some species are strong fighters with long stinging tentacles or powerful chemicals. Others are weaker in a fight but grow fast or cast shade to take the best territory. In nature, this creates a patchwork reef where each coral holds the space it can defend. In aquariums, the same rules apply, but the battlefield is much smaller, so conflicts happen faster and with higher stakes.
How Corals Compete: Space, Light, and Chemistry
Corals compete in three main ways. First, they fight for space by burning or digesting the tissue of neighbors that touch them. Second, they fight for light by growing into shapes that shade others, like plates or domes. Third, they fight with chemistry, releasing compounds into the water that stress or slow competing corals, especially when they are very close.
Why the Hierarchy Matters in Home Aquariums
In a closed tank, every inch matters. A coral that looks peaceful during the day can extend long sweepers at night and sting a neighbor you thought was safe. A fast-growing plating coral can slowly shadow expensive Acropora and stunt them. Soft corals can release chemicals that cause SPS to close up for weeks. If you plan your aquascape and stocking with the hierarchy in mind, you prevent damage before it starts.
The Tools Corals Use in Battle
Stinging Tentacles and Sweeper Tentacles
Many corals have short tentacles for feeding, but some also grow special “sweeper” tentacles when they sense nearby rivals. These sweepers can be much longer than normal and are loaded with powerful stinging cells called nematocysts. They usually come out at night or in low light. For example, Galaxea can send sweepers 12 inches or more, Pectinia often 8 to 12 inches, Hydnophora 4 to 6 inches, and many Euphyllia 2 to 6 inches. These sweepers burn neighboring corals, leaving white patches or receding tissue.
Mesenterial Filaments: Digestive Warfare
Some LPS and SPS corals push out stringy internal filaments that contain digestive enzymes. When these touch a competitor, they begin to digest the neighboring tissue directly on contact. This is common in Favias, Favites, Platygyra, and some chalice corals. It looks like white, stringy slime covering the point of contact, and it can strip tissue quickly.
Shading and Growth Forms
Not all warfare is stinging. Corals like Montipora capricornis grow into wide plates that block light from below. As they expand, the shaded coral weakens and slowly loses ground. Encrusting corals spread like a carpet across rock and can outpace slower neighbors. Branching corals reach into the light and can “escape upward,” but they may shade what is underneath.
Chemical Warfare (Allelopathy)
Soft corals such as leathers (Sarcophyton, Sinularia, Lobophytum) release chemicals, often terpenoids, that stress or inhibit stony corals, especially SPS like Acropora. This chemical pressure can cause poor polyp extension, tissue thinning, and slowed growth. Zoanthids and Palythoa can also release toxins that bother neighbors. Running fresh activated carbon and doing regular water changes helps, but placement still matters.
Who Usually Wins? A Practical Hierarchy
Top-Tier Stingers: Keep Them Isolated
Some corals are famous for long sweepers and aggressive stinging. Galaxea is a powerful fighter that can sting 12 inches or more away. Pectinia (often called Space Invader) is beautiful but sends long, sneaky sweepers mostly at night. Hydnophora grows fast and burns anything it touches. Chalice corals (Echinophyllia, Mycedium, Oxypora) can be calm one day and unleash long sweepers the next. These corals belong on their own “islands,” with wide empty space around them.
Tough LPS Bruisers: Strong, But Predictable
LPS corals like Favia, Favites, Platygyra (maze brain), and some Lobos are strong defenders with short to moderate sweepers. Euphyllia (hammer, torch, frogspawn) have variable aggression; some keep modest reach while others reach far, especially torches. They are less dangerous than Galaxea or Pectinia but still need room. They can deliver painful stings to neighbors and even to your skin.
Shade Masters and Space Takers
Montipora capricornis builds big plates that dominate light. It may not kill by stinging, but it can slowly starve a neighbor of light. Encrusting Montipora and Cyphastrea pave over rock and can creep into territory before you notice. Pavona can also overgrow nearby corals if given the chance.
Soft Corals as Chemical Heavies
Leathers (Sarcophyton, Sinularia, Lobophytum) often win the chemical war. They can irritate SPS across the tank, but especially if placed upstream in the flow. Xenia and Clove Polyps tend to outgrow others by spreading and smothering rather than stinging. Zoanthids and Palythoa spread quickly and can overtake rockwork; some species contain strong toxins and should be handled carefully with gloves and eye protection.
Weaker Fighters, Fast Growers
Many SPS like Acropora and Seriatopora (birdsnest) are not great at close combat. They prefer high light and strong flow to outgrow others. They do best when given their own area with stable water chemistry and low chemical stress. A healthy, fast-growing Acropora can avoid many problems simply by staying out of reach and maintaining strong tissue health.
Mushrooms and Anemones: Special Cases
Corallimorphs (mushrooms) such as Discosoma and Rhodactis can overgrow rock and release mucus that irritates stony corals. They are not strong stingers, but they win by smothering and multiplying. Anemones roam around the rockwork and can sting anything in their path. If you keep an anemone, isolate it from prized corals and expect it to move.
Factors That Change the Pecking Order
Size and Health of the Colony
A bigger, healthier coral almost always has the advantage. Large colonies have more energy for long sweepers and fast regrowth after minor damage. Small frags are easy targets. If you place a small frag near a mature colony of a different species, assume the large colony will dominate unless you give the frag extra space and favorable flow.
Flow Direction and Light Intensity
Flow matters. Strong, directional flow can push sweeper tentacles away from vulnerable neighbors. Low flow allows sweepers to drape over targets. Light changes also shift the balance. A plating Montipora in very high light can expand faster and shade everything beneath it. Adjusting rock orientation or flow nozzles can change who has the upper hand without moving corals.
Nutrients and Feeding
Well-fed LPS grow faster and may extend more aggressive sweepers at night. Heavier feeding can increase competition energy for all corals. Keep nutrients stable and avoid sudden spikes. If you target feed LPS, do it thoughtfully and watch if their reach increases in the following nights. Moderation and consistency reduce surprises.
Time of Day and Colony Maturity
Many corals deploy sweepers after lights out. Things may look peaceful during the day and dangerous at midnight. Also, a coral that was peaceful as a small frag can become aggressive as it matures. Recheck your spacing every few months as colonies grow.
Planning Your Aquascape with Hierarchy in Mind
Zoning the Tank: SPS, LPS, Softies
Divide your tank into zones. Place SPS up high with strong flow and light, away from the heaviest chemical producers. Put LPS in the middle to lower sections with space between colonies. Build a separate “softy island” for leathers, Xenia, and mushrooms. Keeping soft corals downstream of SPS in the flow pattern can reduce chemical impact on sensitive species.
Distance Guidelines for Common Corals
Give dangerous corals more space than you think. Galaxea needs 30 to 45 cm (12 to 18 inches) of clearance. Pectinia often needs 20 to 30 cm (8 to 12 inches). Hydnophora is safer with 15 to 20 cm (6 to 8 inches). Chalice corals usually need 15 to 25 cm (6 to 10 inches). Euphyllia should have 10 to 15 cm (4 to 6 inches), sometimes more for torches. Favia, Favites, and Platygyra do well with 5 to 10 cm (2 to 4 inches). Candy cane (Caulastrea) is gentle and can often sit 5 to 8 cm (2 to 3 inches) from neighbors. Adjust these gaps based on your flow and each coral’s observed reach.
Rock Islands and Sand Moats
Create space with structure. Build separate rock islands for aggressive species and surround them with sand to act as a buffer. If sweepers hang over the sand at night, you will see it before they hit other corals. Islands also help limit the spread of soft corals, mushrooms, and zoas by breaking the rock pathway they use to crawl and multiply.
Height and Shadow Planning
Place plating or encrusting corals where their growth will not shade sensitive neighbors. Keep a vertical gap of 10 to 15 cm (4 to 6 inches) under a Montipora cap before any coral sits below it. Put branching SPS above LPS so the LPS do not shade their base. Think two years ahead: leave room for colonies to triple in size without touching.
Daily and Weekly Management
Observation Routine (Use a Red Light at Night)
Look at the tank 1 to 2 hours after lights out using a dim red flashlight. Many corals do not react to red light, so you can see their sweepers and filaments in action. Note the direction of sweepers and which neighbors are at risk. Make small adjustments early rather than waiting for damage to appear.
Pruning and Fragging with a Plan
Trim fast growers before they make contact. Cut Montipora plates back from the edge you want to protect. Frag encrusters before they cross onto another rock. When cutting, use clean tools and glue fresh frags to a frag rack or separate rock. Trade or rehome extras so you maintain safe spacing in the display.
Moving Corals Safely
Move corals during the day when sweepers are retracted. Wear gloves and eye protection, especially with zoanthids and palys. Avoid dragging tissue across rock. If two corals have already burned each other, separate them and improve flow. Do not place a freshly injured coral next to a strong stinger; give it a quiet spot to heal.
Carbon, Skimming, and Water Changes for Chemical Control
To reduce soft coral chemicals and general dissolved organics, run activated carbon and keep up with water changes. A common starting point is 0.25 to 0.5 cup of high-quality granular activated carbon per 50 gallons (190 liters), replaced every 2 to 4 weeks. In soft-heavy tanks, many hobbyists use closer to 1 cup per 50 gallons and change it every 2 weeks. Strong protein skimming and periodic use of a PolyFilter pad help as well. If you add a big leather coral or notice “yellowing” water, refresh carbon and do a larger water change.
Flow Tuning to Manage Sweepers
Point flow so that sweepers bend away from vulnerable neighbors. A gyre or wavemaker can be angled to carry sweepers into open water or a sand gap rather than into an SPS colony. Avoid dead zones where sweepers can drape and stick to a target all night.
Troubleshooting Common Clashes
Burnt Tips and Tissue Recession
If you see white, freshly exposed skeleton or sharp “burn” lines on one side of a coral, suspect a stinging neighbor. Move one coral or increase the gap. Check at night to see the attacker in action. Improve flow and consider a small iodine-based dip for the injured coral if tissue is infected, but remember dips do not solve ongoing aggression.
Soft Coral Chemical Blues
If SPS show poor polyp extension, dull color, or slow growth after adding leathers, run fresh carbon, do a 20 to 30 percent water change, and reposition the leather downstream in the flow. In some cases, you may need to separate soft corals to their own island or even a separate tank to keep sensitive acros happy.
Surprise Sweepers from “Peaceful” Corals
Some corals seem calm for months and then extend long sweepers overnight. This happens with chalices, Pectinia, and even some Euphyllia. If this occurs, give them more space immediately. Feeding these corals heavily can increase their energy and encourage stronger responses, so moderate feeding if aggression becomes a problem.
Anemone Walkabouts
When anemones move, they sting whatever they touch. Protect high-value corals by isolating the anemone on its own rock island with a sand moat or by dedicating a section of the tank to it. Cover wavemaker intakes to prevent shredding. If an anemone starts drifting, dim lights slightly and reduce flow to encourage it to settle, then slowly restore normal conditions.
Sample Stocking and Layout Plans
SPS-Dominant Mixed Reef
Place Acropora and birdsnest high with strong, turbulent flow. Keep leathers and mushrooms off the main rockwork on a small island downstream of SPS. Use encrusting Montipora on the back wall where it cannot shade acros below. Avoid Galaxea and Hydnophora entirely, or isolate them far away on their own rocks with at least 30 cm (12 inches) of space. Run activated carbon monthly and change it often. Keep nutrients stable and low to moderate to favor SPS health.
LPS Garden with Safety Margins
Choose moderate-aggression LPS like Acanthastrea (Micromussa lordhowensis), Caulastrea, and some Favia for a colorful garden. Space colonies 5 to 10 cm (2 to 4 inches) apart and watch for sweepers at night. Place torches, hammers, and frogspawn at the edges of the garden with 10 to 15 cm (4 to 6 inches) gaps. Put any chalice or Pectinia on a separate shelf rock with a sand moat below. Feed LPS moderately and maintain gentle, random flow.
Soft Coral Showcase
Build a leather island with Sarcophyton and Sinularia, and keep mushrooms and zoas on their own rocks. Because chemical output can be high, use more carbon and do consistent water changes. Keep any SPS in a different zone or skip them entirely. Control spread by trimming back stolons and peeling mushrooms before they reach the main rockwork. This style can be beautiful, lower light, and very active with flow.
Myths and Realities of Coral Dominance
Myth: “All Euphyllia Are Peaceful”
Reality: Euphyllia can be moderate to highly aggressive. Torches often reach farther and hit harder than hammers or frogspawn. Mixed Euphyllia can sometimes touch each other within the genus, but cross-species contact can still cause damage. Give them space and watch at night.
Myth: “Acros Always Win”
Reality: Acropora are poor close-range fighters. They win by staying healthy, growing fast, and staying out of reach. Place acros where they get high light and flow and where neighboring LPS cannot touch them. Keep chemical stress low by managing soft corals and organics.
Myth: “More Flow Stops Sweepers Entirely”
Reality: Flow can redirect sweepers, but it does not remove the threat. In low flow, sweepers drape and burn. In high flow, they may whip around and still tag neighbors. Use flow to your advantage but keep physical distance as your main safety strategy.
Pro Tips from the Trenches
Use Frag Racks as a Staging Area
When you buy a new coral, place it on a frag rack for a week or two. Watch its nighttime behavior and check for pests. This gives you time to plan a safe spot without risking a surprise attack on your established colonies.
Plan for the Future Size, Not the Frag Size
Most conflicts happen because we forget how big corals get. A small chalice or Hydnophora looks harmless today but becomes a problem in six months. Leave wide margins from day one, and you will avoid constant rescapes later.
Match Neighbors by Strategy
Put strong stingers in corners or on isolated ledges where they have fewer neighbors. Place gentle corals near each other. Pair fast growers with other fast growers so they meet at equal strength. Keep softies on a separate rock system if you love SPS.
Watch for Yellow Water as a Chemical Clue
If your water takes on a yellow tint when viewed through a white bucket or glass, dissolved organics are building up, often from soft coral chemicals and food. Refresh carbon and consider a larger water change. Clear water often brings immediate improvement in polyp extension for SPS.
Conclusion
Coral dominance hierarchy is not a mystery once you know the rules. Corals compete for space, light, and chemical advantage, and some are far more aggressive than others. Plan your reef with this in mind: isolate the heavy hitters, leave real space between colonies, manage chemicals with carbon and water changes, and check your tank at night to catch conflicts early. Build zones for SPS, LPS, and soft corals so each group thrives. When in doubt, give more room than you think you need and think two years ahead. With a clear strategy and steady observation, you can enjoy a mixed reef where beauty, growth, and harmony are the natural result of smart planning.