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Corals do not share space well. In a reef tank, they compete, push, sting, and shade. If you ignore this, the tank slowly turns into a battlefield. If you understand coral dominance hierarchy, you can plan space, flow, and stocking so your corals grow without constant damage.
This guide shows how coral dominance works, what tools corals use to fight, which groups usually win, and how to build a layout that holds the peace. You will see clear spacing rules, practical setups, and fast responses when conflict starts. Keep reading and use each section as a checklist for your own aquarium.
What Coral Dominance Hierarchy Means in a Reef Tank
Dominance hierarchy is the order in which corals control space when they meet. It is not a single ladder. It shifts with species, size, health, light, and flow. A coral that wins in one spot can lose in another. Think of many small territories across your rockwork.
Four drivers set the rank in any spot:
1) Aggression strength such as stings and chemical output
2) Growth rate and growth shape
3) Ability to shade or overgrow neighbors
4) Stability of the environment that favors one group over another
Common patterns:
– Many large polyp stony corals are strong at direct stinging.
– Some soft corals are powerful at chemical warfare.
– Fast encrusting or plating corals win by covering and shading.
– Branching small polyp stony corals win by fast vertical growth but lose to close stings.
Aggression Tools Corals Use
Stinging and Sweeper Tentacles
Many corals extend long sweeper tentacles after lights out. These can reach far beyond the daytime tissue.
Typical reach and spacing guidelines:
– Euphyllia such as hammer and torch: keep 8 to 15 cm from neighbors
– Favia and Favites: keep 10 to 20 cm
– Galaxea: keep 20 to 30 cm or more
Watch at night with a dim blue light. If sweepers are touching, increase distance or change flow so tentacles do not drift onto neighbors.
Mesenterial Filaments
Some corals extrude white, stringy filaments from the mouth or skeletal edges. These digest neighbor tissue on contact. This often appears after a direct fight. If you see white strings on a neighbor, separate the colonies the same day.
Chemical Warfare
Soft corals such as Sarcophyton and Sinularia release compounds that stress or slow nearby corals. You cannot see this, but you can manage it. Run activated carbon, keep good protein skimming, and do regular water changes. Place soft corals downflow from sensitive small polyp stony corals.
Overgrowth and Shading
Some corals win by spreading over rock or by layering plates that block light. Examples are Montipora plating over neighbors and green star polyps spreading across rock and glass. Mushrooms and rhodactis can smother by expanding and touching. Plan borders and trim often.
Mucus Sloughing and Bacterial Stress
When stressed, leathers and some large polyp stony corals shed mucous films. These can irritate neighbors and feed bacteria. Keep flow steady, siphon loose slime, and increase carbon during heavy sloughing.
Species Groups and Typical Rank
Soft Corals and Corallimorphs
– Leathers such as Sarcophyton and Sinularia: strong chemical output. They do well across a range of light. Keep them downflow from small polyp stony corals and run carbon full time.
– Green star polyps and xenia: very fast spread. Weak sting but strong space gain. Isolate on an island and trim monthly.
– Mushrooms and rhodactis: can smother by expansion. Keep a rubble border. Avoid placing them next to acropora or fleshy large polyp stony corals.
– Zoanthids and palythoa: spread by matting. Sting is weak. They can shade bases of branching corals over time.
Large Polyp Stony Corals
– Euphyllia such as hammer, frogspawn, torch: moderate to strong sweepers. Keep 8 to 15 cm spacing. They can coexist with each other if same species and disease free, but watch for contact burns anyway.
– Favia and Favites: long sweepers at night. Keep 10 to 20 cm spacing. Place on separate rocks if possible.
– Galaxea: very aggressive sweeper reach. Keep 20 to 30 cm or more. Best on a separate island.
– Micromussa and Acanthastrea: moderate aggression near tissue. Keep 5 to 8 cm spacing and avoid contact.
– Scolymia and Cynarina: large flesh, strong near field sting but sensitive to damage. Give a clear buffer so nothing brushes them.
Small Polyp Stony Corals
– Acropora: fast vertical growth when stable. Weak in direct sting battles. Place away from aggressive large polyp stony corals. Give 5 to 10 cm between colonies for growth room.
– Montipora: plating and encrusting forms that shade and overrun. Can outcompete by growth but lose to direct stings. Control edges with trimming.
– Pocillopora and Stylophora: can spread and overgrow nearby branches. Keep space between them and acropora to avoid cross contact.
Reading the Tank: Signs the Hierarchy Is Shifting
Check daily for early signs of conflict:
– Polyp retraction on one side of a coral
– White or gray burn lines where tissues touch
– Visible sweeper tentacles reaching neighbors after lights out
– White strings that look like guts on a neighbor
– Excess slime strings drifting in flow
– Tissue recession or bare skeleton along a shared border
– A coral growing away from a neighbor or turning its growth tip
When you see these, adjust spacing, flow, or placement the same day.
Plan Your Aquascape With Hierarchy in Mind
Create Islands and Borders
Build separate rock islands for groups that do not mix. Put strong stingers such as Galaxea on their own island. Keep fast spreaders like green star polyps on a single rock with sand all around. Use rubble moats or bare sand strips to slow mats and encrusters.
Place by Height and Flow
Put soft corals that release chemicals downflow from sensitive small polyp stony corals. Place small polyp stony corals higher where light is stronger and sweepers from large polyp stony corals are less likely to reach. Keep aggressive large polyp stony corals on mid to lower rock where you can give them space.
Reserve Growth Lanes
Leave empty zones between colonies so they have room to grow without contact. A 5 to 10 cm empty ring around small polyp stony corals and a 10 to 20 cm ring around aggressive large polyp stony corals prevents most conflicts.
Spacing Rules That Work
Use these starting distances and adjust after night checks:
– Euphyllia to any neighbor: 8 to 15 cm
– Favia or Favites to any neighbor: 10 to 20 cm
– Galaxea to any neighbor: 20 to 30 cm or a separate island
– Micromussa or Acanthastrea to any neighbor: 5 to 8 cm
– Small polyp stony coral to small polyp stony coral: 5 to 10 cm
– Mushrooms, green star polyps, xenia: isolate on an island with sand gaps
– Leathers relative to small polyp stony corals: place at least 25 to 40 cm downflow
Flow and Light as Controls
Use Flow to Control Contact
Stronger, more chaotic flow can limit how far sweepers hang in one direction. Aim flow so tentacles blow back on the aggressor rather than onto a neighbor. Avoid laminar streams that carry sweepers across a gap and plant them onto another coral at night.
Use Light to Shape Growth
Plating Montipora expands fastest under strong even light. If you must keep them, put them where their shade does not fall on prized branching corals. Keep fast spreaders in zones with edges exposed to lower light or sand so they slow at the border.
Filtration and Chemical Control
Activated Carbon and Skimming
Run activated carbon 24 or 7 to reduce chemical warfare. Place the bag or reactor in high flow. Change it weekly in small amounts or every two weeks in a larger amount. Keep the protein skimmer tuned to remove organics that carry allelopathic compounds.
Water Changes and UV
Do regular water changes, such as 10 to 15 percent weekly or every two weeks, to dilute irritants. UV can polish water clarity and may help reduce free floating irritants, but spacing and carbon do more for coral conflicts.
Feeding and Growth Balance
Feeding Drives Aggression
Spot feeding large polyp stony corals increases growth and sweeper length. If you feed them, hold proper spacing and watch night behavior. Feed modestly one or two times per week. Rinse frozen foods to limit extra nutrients.
Keep Nutrients Stable
Very low nutrients make many corals fragile. Stable moderate nutrients support tissue strength. As a safe starting point, aim for nitrate in the range of 5 to 15 ppm and phosphate in the range of 0.03 to 0.1 ppm. Keep these stable rather than chasing exact numbers.
Acclimation, Quarantine, and Introduction Order
Dip and Observe New Corals
Coral dips remove pests that can stress or injure neighbors. Quarantine if you can. At minimum, dip and inspect every base and crevice. Pests trigger stress, and stressed corals fight harder.
Use Frag Racks to Test
Place new frags on a rack for one to two weeks. Watch night extension, polyp behavior, and sweepers. Move to rock only when you know its reach and response to flow.
Introduce Least Aggressive First
Let peaceful or slow growers settle first. Add aggressive corals later. A mature colony can resist better than a fresh frag.
Maintenance Routines to Hold the Line
Trim and Redirect Growth
Clip plating Montipora edges before they shadow neighbors. Peel back green star polyps and xenia monthly. Use bone cutters to remove Euphyllia heads that are drifting into another coral. Small, frequent trims are easier than emergency rescues.
Set Physical Barriers
Use bare sand strips, rubble moats, or small epoxy walls to stop mats from crossing. Place loose rubble around mushrooms so you can remove stray clones before they reach key areas.
Case Layouts That Work
Mixed Reef Strategy
– Top and high flow: small polyp stony corals on separate mounts, 5 to 10 cm apart
– Mid rock: moderate large polyp stony corals such as Euphyllia with 8 to 15 cm buffers
– Low rock: micromussa and acanthastrea with 5 to 8 cm gaps
– Separate islands: green star polyps, xenia, and Galaxea with sand all around
– Filtration: carbon 24 or 7, skimmer tuned, regular water changes
SPS Dominant Strategy
– Keep soft corals off the main rockwork
– Place any large polyp stony corals on side islands away from acropora
– Reserve empty lanes between colonies and trim Montipora often
– Maintain moderate nutrients and stable alkalinity for strong tissue
Soft Coral Garden Strategy
– Group leathers together in strong flow to move mucus away
– Keep mushrooms on separate rocks with sand borders
– Run extra carbon and keep up with water changes
– Avoid adding sensitive small polyp stony corals into this system
Troubleshooting Conflicts Fast
If Two Corals Are Touching
– Increase distance the same day if possible
– Change flow so sweepers do not blow onto the weaker coral
– Gently baste away slime and filaments with a turkey baster
– Move one coral to a frag rack to recover
– Add fresh activated carbon and increase aeration and skimming
– Perform water changes totaling 30 to 50 percent over two days
– Reduce light intensity by about 20 percent for three to four days to lower stress
– If tissue is damaged, trim dead margins to clean skeleton so bacteria do not spread
Track the Hierarchy Over Time
Map and Monitor
Keep a simple coral map and note distances. Check at night once a week for sweeper reach. Log any burns and what fixed them. Small adjustments early prevent big losses later.
Conclusion
Coral dominance hierarchy is always active in a reef tank. When you learn how corals fight and how fast they grow, you can plan space, flow, and maintenance to keep the peace. Use clear spacing rules, isolate aggressive or fast spreading species, run carbon, and trim on schedule. Watch at night, act early, and let each coral hold a safe territory. A stable, balanced layout grows faster and looks better because the corals are not wasting energy in constant conflict.
FAQ
Q: What is coral dominance hierarchy in a reef tank?
A: It is the order in which corals control space when they meet, driven by aggression strength, growth rate, shading, and environment. It shifts by species, size, health, light, and flow, and plays out across many small territories on your rockwork.
Q: How far apart should I place aggressive large polyp stony corals?
A: Use these starting distances: Euphyllia 8 to 15 cm, Favia or Favites 10 to 20 cm, and Galaxea 20 to 30 cm or a separate island. Adjust after night checks of sweeper reach.
Q: What tools do corals use to compete?
A: They use stinging and sweeper tentacles, mesenterial filaments, chemical warfare, overgrowth and shading, and mucus sloughing that can irritate neighbors.
Q: How can I reduce chemical warfare from soft corals?
A: Run activated carbon 24 or 7 in high flow, keep protein skimming strong, do regular water changes, and place soft corals downflow from sensitive small polyp stony corals.
Q: What should I do if two corals start attacking each other?
A: Increase distance the same day, redirect flow, baste away slime, move one coral to a frag rack, add fresh carbon, perform water changes totaling 30 to 50 percent over two days, reduce light by about 20 percent for three to four days, and trim dead margins if needed.