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Corals may look calm and gentle, but beneath the surface they are always competing. In the ocean and in our aquariums, corals fight for space, light, food, and flow. New hobbyists often ask whether there is a “dominance hierarchy” among corals, like pecking orders in birds or social ranks in mammals. The short answer is that there is no single ladder that works for every coral in every tank. Instead, there are patterns and predictable matchups. Some corals win by growing fast and smothering neighbors. Others win with long, stinging sweepers or powerful chemicals. Understanding these strategies helps you plan your aquascape, prevent coral wars, and build a mixed reef where everything thrives.
What “dominance hierarchy” really means for corals
Competition without brains: how corals “decide” who wins
Corals are animals, but they do not have brains, social groups, or behavior in the way fish do. Their “decisions” are automatic responses wired into their biology. When corals meet a competitor, they release chemical signals, extend specialized tentacles, or grow in certain directions. Over days to weeks, one coral gains ground while the other retreats or dies back. Dominance is not about status; it is about which coral can claim and keep resources. In tanks, this competition is amplified because space is limited and flow pushes their tentacles together more often than on a wide reef.
Space, light, flow, and nutrients: the currencies of coral power
Corals trade in four currencies. Space is the foundation, because corals need rock or substrate to attach and expand. Light fuels the symbiotic algae (zooxanthellae) living inside many corals, so shaded corals slow down or starve. Flow delivers oxygen and nutrients while carrying away waste; low flow can allow chemical toxins to build up, while high flow boosts polyp health but can also carry stingers farther. Nutrients and trace elements support growth and recovery. A coral that controls space and light, in favorable flow and stable water chemistry, tends to dominate.
The main tools corals use to dominate
Sweeper tentacles and stinging cells
Many large polyp stony corals (LPS) and some soft corals extend long sweeper tentacles that carry powerful stinging cells called nematocysts. These sweepers can reach several inches beyond the coral’s body at night. Galaxea, Pectinia, Hydnophora, and some Favia species are famous for sweepers that can burn nearby corals and cause rapid tissue loss. Euphyllia (torch, hammer, frogspawn) also sting effectively, especially torches, although their reach is usually shorter than Galaxea. These sweepers often come out under low light or after lights-out, which is why nighttime spacing matters.
Mesenterial filaments and digestive aggression
Some corals can extrude inner digestive filaments directly onto a neighbor, dissolving tissue and leaving bare skeleton behind. This is not just a sting; it is chemical digestion. Favids, some brains, and even certain SPS can do this when in sustained contact. In a tank, you might notice stringy white filaments on a point of contact and a receding scar the next day. If the attacking coral repeats this, the victim may lose entire branches or plates.
Overgrowth, shading, and skeletal warfare
Fast-growing corals, especially branching SPS and mat-forming soft corals, dominate by occupying space quickly. Montipora capricornis can plate outward, shading light from slower competitors. Encrusting corals can pave over rock and smother slower LPS around their base. Some corals grow thicker skeleton walls that push neighbors aside; others grow under and then over, trapping slower corals in the dark. This is a silent but effective method of control that can continue even if stinging is minimal.
Chemical warfare (allelopathy)
Soft corals such as Sinularia, Sarcophyton, Lobophytum, and some zoanthids release allelopathic compounds that can slow growth or stress neighbors. You may not see a visible attack, but nearby corals stay retracted, fade in color, or show tissue thinning. In mixed reefs, allelopathy can be the hidden reason why an SPS refuses to thrive despite good numbers. Activated carbon and strong skimming help reduce these compounds, but placement and water movement matter just as much. Remember that zoanthids and palythoas also carry palytoxin, which is dangerous to humans; handle them with eye and skin protection, and never scrub them with hot water or steam.
Microbial and mucus tactics
Corals host diverse microbiomes. When corals stress each other, the slime and mucus they shed can carry bacteria that tip the balance in favor of one coral and against another. High organics and low flow increase this risk. While less visible than stinging, these microbial shifts can cause sudden tissue loss in a coral that otherwise looks uninjured. Good flow and filtration reduce this risk and help keep the peace.
Are there clear hierarchies? The nuanced answer
Think “guilds” rather than one universal ladder
There is no single top-to-bottom ranking that applies to all tanks. Instead, corals fall into broad guilds with typical strategies. Long-sting LPS often beat SPS in close-quarters combat because sweepers reach farther than delicate SPS can handle. Fast-growing softies can overrun slow LPS if allowed to creep, even without stinging. Some SPS defeat other SPS by outgrowing or overshadowing them. These guild trends form a loose hierarchy, but outcomes vary with conditions, size, and placement.
Context matters: size, flow, structure, and maturity
A tiny frag of a “tough” coral can still lose to a big colony of a “weaker” coral. High, chaotic flow blunts sweeper reach but can spread allelopathic chemicals. Rockwork with overhangs favors shaders like plating Montipora, while open bommies give sweepers more room to reach. A mature tank with stable parameters can support more mixed neighbors than a new system where stress magnifies chemical effects.
Health, nutrition, and recovery speed tip the balance
Well-fed corals with stable alkalinity, calcium, magnesium, and trace elements recover faster from minor stings. A coral that bounces back overnight can tolerate occasional skirmishes, while a stressed coral loses ground with each encounter. Consistent parameters, adequate phosphate and nitrate (not zero), and proper lighting intensity improve resilience and reduce the “winner takes all” dynamic.
Typical coral guilds and how they dominate
Fast growers and creepers: Xenia, green star polyps, Kenya tree, zoanthids
These corals often win by covering rock quickly. Xenia and Kenya tree can shade and crowd neighbors by swaying into them, and their fragments reattach where they land. Green star polyps form mats that crawl over adjacent surfaces. Zoanthids spread in patches and can chemically inhibit nearby SPS. Their stinging is modest, but their growth and chemistry make them deceptively dominant in small tanks. Keep them on isolated “islands” or separate rocks if you want to contain them.
Long-sting LPS: Galaxea, Pectinia, Hydnophora
These are the classic bullies of close combat. Galaxea develops long, powerful sweepers that can reach several inches, especially at night. Pectinia (sometimes called chalice-like but different) can send out stingers and filaments. Hydnophora has potent polyps that burn most neighbors within reach. Place them where they cannot touch prized SPS or fleshy LPS. Give them room down-current since sweepers tend to drift with the flow.
Medium-sting LPS: Euphyllia, Favia, Favites, Acanthastrea, Platygyra
Euphyllia species have moderate to strong stings; torches are usually the most aggressive, then hammers and frogspawns. Favids can fight using both sweepers and digestive filaments at close range. Acanthastrea and Platygyra defend their boundaries but are often vulnerable to long-reach neighbors. These corals coexist best with careful spacing and similar neighbors, avoiding direct contact. Do not mix torches with delicate fleshy LPS like Trachyphyllia or Scolymia in tight quarters.
SPS branchers and platers: Acropora, Montipora, Pocillopora, Stylophora, Seriatopora
SPS often lose to LPS stings at close range but can win by growth and shading. Plating Montipora shade upward neighbors and can encrust into bases of other corals. Branching Acropora can overtop slower neighbors and reclaim light. Some SPS also sting lightly or use filaments when in contact with other SPS. Many Acropora are sensitive to allelopathy from softies, so placing them up-current and away from leather corals reduces stress. Stability and strong flow help SPS hold their ground.
Non-photosynthetic (NPS) and special cases
NPS corals like Tubastrea (sun corals) and Dendronephthya do not rely on light. Their dominance is rarely about stinging; it is about feeding access and shade tolerance. They prefer lower light zones with targeted feeding. They usually do not overrun neighbors, but they can suffer if placed near aggressive LPS. Sponges and macroalgae can also compete for space and alter flow around corals; manage them so they do not smother coral bases.
Practical placement and aquascape strategies
Zone your tank by aggression and growth style
Create zones that cluster similar behaviors together. Place fast-growing softies on isolated rocks near the sand or on separate islands so they cannot creep onto your main reef structure. Reserve a mid-level zone for moderate LPS that can coexist with careful spacing. Keep SPS on higher, brighter structures with strong flow to favor their growth strategy and dilute soft coral chemicals. If you insist on mixing everything, physical separation with islands is your best friend.
Spacing rules of thumb that actually work
Leave 15 to 20 cm (6 to 8 inches) around corals known for long sweepers like Galaxea and Hydnophora. Give Euphyllia at least 10 to 15 cm (4 to 6 inches) to any neighbor, more if downstream. For Favias and similar LPS, 5 to 10 cm (2 to 4 inches) is usually safe if you maintain stable parameters and watch night behavior. For SPS-to-SPS spacing, 2 to 5 cm (1 to 2 inches) can work, but plan for growth and keep fast platers from overshadowing prized sticks. Always observe after lights-out to confirm you are not underestimating reach.
Flow lanes and shadow management
Arrange powerheads so that long sweepers do not blow into vulnerable corals. If you can, aim for alternating flow patterns that mix the water without pushing tentacles in a single direction all night. For shading, avoid placing slow-growing or light-hungry corals directly under plating Montipora or dense Acropora tables. Use shelves and arches consciously: plates go higher, fleshy LPS lower and more open, softies on separate perches that do not feed shade onto SPS zones.
Islands, moats, and walls
Use sand gaps as “moats” that creeping softies will have trouble crossing. Build islands with rubble edges that you can lift out and trim if a coral starts to overrun its space. Place the most aggressive stingers on the down-current edges of rocks facing open water, so their sweepers have little to hit. Consider vertical separations: a tall SPS bommie upriver from a lower softy island reduces chemical stress on the SPS.
Managing chemical rivalry
Activated carbon and media rotation
Run high-quality activated carbon in a reactor or high-flow media bag to absorb allelopathic compounds from soft corals and zoanthids. Replace small amounts frequently rather than a large amount infrequently; for example, change 25 to 50 percent of the carbon every two weeks to keep adsorption consistent without shocking the system. Rinse new carbon well to prevent dust. If you add or prune a large leather coral, refresh carbon preemptively.
Water changes and strong protein skimming
Regular water changes dilute dissolved organics and stabilize trace elements that support recovery after minor coral skirmishes. A reliable protein skimmer helps remove organics and some hydrophobic compounds. Skimming also oxygenates water, which benefits all corals and reduces stress under chemical competition. Keep nitrate and phosphate in a reasonable range rather than driving them to zero; extremely low nutrients can make corals fragile and less able to heal.
Ozone and UV, used thoughtfully
Ozone in a properly controlled skimmer can improve water clarity and reduce some organics, but it must be used carefully with an ORP controller and carbon on the skimmer outlet. UV sterilizers reduce free-floating bacteria and algae, helping stabilize the microbial environment during coral conflicts. Neither ozone nor UV replaces carbon and water changes, but they can be useful tools in heavily stocked mixed reefs.
Introducing new corals without starting a war
Quarantine, dips, and safety
Quarantine new corals for pests and to observe their behavior. Use coral dips to remove hitchhikers such as flatworms and nudibranchs. Handle zoanthids and palythoas with gloves and eye protection due to palytoxin risk; never scrub them with hot water, and keep them away from cuts or eyes. Quarantine also lets you acclimate corals to your lighting and water chemistry without immediate competition from established neighbors.
Order of introduction and initial placement
In a brand-new tank, start with easier, less aggressive corals and allow them to settle. Add the most aggressive long-sweeper LPS last, after the rockwork is stable and territories are clear. Initially place new corals with extra spacing, observe for a week of day and night cycles, and then adjust positions. Mount encrusters on dedicated tiles or islands so they do not run into prized colonies as they grow.
Nighttime checks and monitoring
Use a dim blue flashlight after lights-out to see sweeper length and polyp extension. Many corals look peaceful by day but deploy full weapons at night. If you see sweepers reaching farther than expected, move the victim coral or redirect flow. Re-check after any new addition, pruning, or lighting change, as these events can trigger new behaviors.
When corals touch: reading signs and first aid
Early warning signs of trouble
Watch for localized tissue recession, pale or browned tips facing a neighbor, stringy white filaments, excessive mucus, and persistent polyp retraction on the side nearest another coral. Discoloration lines or a “burn” track usually indicate stinging. A dull, dusty look and reduced extension over days suggest chemical stress. Catching these early makes saving the coral much easier.
Emergency moves and frag rescues
If a coral is burning a neighbor, separate them immediately. Even a temporary move to the sand bed helps. For SPS tips that are burned, clip back to clean tissue with coral cutters and improve flow to the area. For LPS with a localized sting, gently turkey-baste away dead tissue and ensure no detritus collects in the wound. Iodine-based dips can help reduce infection risk after aggressive contact. After an event, stabilize alkalinity and keep nutrients steady; do not make dramatic parameter changes unless something is clearly out of range.
Long-term fixes and prevention
Adjust the aquascape to create lasting borders. Increase carbon and perform a small series of water changes over a week if you suspect allelopathy. Consider moving the aggressor down-current or onto its own rock. Trim fast-growing corals regularly; consistent pruning prevents forced conflicts later.
Example matchups: who tends to win and why
Galaxea versus Montipora plating
Galaxea usually wins if their sweepers can reach the plate. The stings cause rapid tissue loss on the Montipora. However, if the Montipora is higher and well out of reach, it can shade the Galaxea over time, causing the stinger to retract and weaken. Solution: keep at least 15 cm of clearance and avoid putting Monti plates directly down-current of Galaxea.
Euphyllia torch versus Acropora brancher
Torch corals often burn nearby Acropora tips. The Acro can recover if the torch is not too close and if you maintain strong flow and stable alkalinity. With enough distance, the Acropora may eventually overtop the torch in height, but the risk of repeated tip burn is high. Solution: give torches 10 to 15 cm clearance and place Acros up-current or higher in strong, randomized flow.
Zoanthids versus Favia or Acanthastrea
Zoanthids rarely sting hard enough to kill a healthy Favia or Acan head-on, but they can creep around and chemically irritate them, leading to poor extension and slowed growth. Over months, the zoas occupy the available rock and trap the LPS in a smaller area. Solution: keep zoas on their own island and trim back mats before they approach LPS bases; run carbon consistently.
Soft leather corals versus SPS
Large Sinularia or Sarcophyton can release compounds that cause SPS to fade or stop growing, even without touching. SPS placed down-current of a big leather sometimes show chronic poor color until the leather is moved or carbon use is increased. Solution: keep leathers on the opposite side of the tank from sensitive SPS, maximize flow and skimming, and rotate fresh carbon.
Myths and misconceptions
“All soft corals are peaceful”
This is false. While many softies lack powerful stings, they dominate by fast growth and chemical means. Xenia, green star polyps, and large leather corals can outcompete and suppress stony corals in small or low-flow tanks.
“The coral with the bigger sting always wins”
Not always. Placement, size, light, and flow can flip outcomes. A well-placed SPS colony in strong flow and bright light can outgrow a medium-sting LPS below it, avoiding contact. Conversely, even a small long-sweeper coral can devastate a large SPS if placed too close down-current.
“You can mix anything in a nano if you trim often”
Space is the toughest currency in a nano tank. Frequent trimming helps, but nighttime stings and chemical pulses after pruning can still cause chain reactions. Careful stocking and conservative spacing are even more important in small volumes.
Building a peaceful mixed reef
Plan a stock list by zones and strategies
Decide early which corals are the stars and give them the best real estate. If you want SPS dominance, place softies and aggressive LPS on separate islands or in lower, down-current zones, and commit to regular carbon and strong flow. If you love fleshy LPS gardens, keep torches separated, choose moderate neighbors like hammers and frogspawns in one area, and avoid encroaching encrusters nearby. For a soft coral showcase, design islands with sand gaps and leave the main rock free for a few feature pieces.
Maintenance rhythm that prevents conflict
Stability prevents escalation. Keep alkalinity steady within a narrow range. Use a reliable schedule for water changes and carbon replacement. Inspect at night weekly for sweeper reach and adjust flow accordingly. Trim creeping mats monthly before they approach boundaries. Quarantine and dip all new additions. When in doubt, add space rather than squeezing corals in; tanks look fuller and healthier when corals have room to grow naturally.
Conclusion
There is no single, universal dominance hierarchy among corals, but there are reliable patterns. Some corals rule with long sweepers, others with speed and shade, and still others with subtle chemical influence. The “winner” in your tank depends on size, placement, flow, light, and stability. If you think in terms of guilds and strategies rather than rigid rankings, you can design a reef where the right corals occupy the right spaces, and conflicts are rare and controllable. Plan your zones, respect spacing, manage chemical load with carbon and good filtration, and observe your reef after dark. With these habits, you can enjoy a thriving, mixed coral community that grows for years with minimal drama, proving that while corals do compete, smart aquascaping and care can turn rivals into stable neighbors.