Overview
Acropora-Eating Flatworms (Amakusaplana acroporae), usually shortened to AEFW, are one of the most dreaded SPS pests in reefing — and for good reason. Unlike nuisance flatworms that mostly annoy things, AEFW are true coral predators that feed on Acropora tissue. They can slowly strip color, stunt growth, and eventually kill colonies if they’re not caught early.
The hard part is they’re sneaky. Early on, you often don’t see the worms. You just see that something feels “off” with your Acros: reduced polyp extension, patchy color, dullness, or weird bite-like marks. By the time you spot them, they may already be established.
If you keep Acropora and you add frags, AEFW prevention habits are not optional — they’re part of the SPS game.
Quick Care Snapshot
Common Name: Acropora-Eating Flatworm (AEFW)
Scientific Name: Amakusaplana acroporae
Reef Safe: No (predator of Acropora)
Difficulty: Easy for them, hard for us
Target Host: Acropora spp.
Where They Hide: On Acropora branches, undersides, bases, and in crevices
Reproduction: Eggs laid on/near Acropora bases and shaded surfaces
Primary Signs: Bite marks, reduced PE, patchy tissue loss, sudden decline in Acros
Main Risk: Spreads through frag trading and adding unvetted Acropora
Natural Background
AEFW are small flatworms adapted to live on coral colonies and feed on them. In the wild, predators and natural checks keep many coral pests from becoming a takeover. In our tanks, those checks often don’t exist — and Acropora colonies are concentrated and accessible.
In reefing, AEFW are largely a frag-transfer problem: they move from system to system when we add Acropora pieces (or anything attached to them) without strict inspection and quarantine habits.
Tank Requirements
AEFW don’t have “tank requirements” the way livestock do — their requirement is simply: Acropora is present. If you have Acros, your system can support them.
They thrive when:
• New Acropora is added regularly
• Frags go straight into the display
• There’s no consistent dipping + inspection routine
• Colonies have dense branch structure and shaded areas
Where to look
• The underside of Acropora branches
• Around the base where the coral meets rock or plug
• Shaded crevices behind colonies
• Anywhere you can’t easily see without removing the frag
Feeding
AEFW feed on Acropora tissue. That’s the whole issue. They aren’t scavengers and they aren’t just “annoying.” They consume coral tissue and stress the coral continuously.
Because they’re feeding on the coral itself, you don’t “starve” them out with nutrient control. The only “food control” is controlling their access to Acropora — which usually means controlled handling and containment habits.
Compatibility
With corals
• Acropora: Primary target. Some Acropora seem to get hit harder than others, but assume all are vulnerable.
• Other SPS/LPS/Soft corals: Typically not the target, but they can hitchhike on plugs/rockwork and survive long enough to transfer.
With fish/inverts
Most fish ignore them. Some wrasses may pick at pests, but relying on “something will eat them” is not a strategy. Even if something eats some, it often won’t break the life cycle if eggs are present.
Common Mistakes
1) Adding Acropora directly to the display
This is how AEFW become a tank problem. One frag can introduce them.
2) Dipping once and thinking you’re safe
Dips can help remove adults, but eggs are the trap. Egg clusters are usually resistant to typical dips. That’s why single-dip confidence is dangerous.
3) Missing the early signs
People often chalk early symptoms up to:
• lighting changes
• flow issues
• parameter swings
• random “Acro mood”
Meanwhile, the coral is literally being eaten.
4) Only inspecting the top/visible side
AEFW love the underside and base areas because it’s protected. If you don’t inspect those zones, you’re basically inspecting the “least likely” place.
5) Not treating the system as a system
If you discover AEFW on one Acro, assume:
• other Acros have been exposed
• egg clusters may exist in multiple spots
• you’re dealing with a lifecycle, not a single animal
Notes & Variations
What hobbyists usually see (the practical signs)
• Bite marks: often appear as irregular pale patches or “chewed” areas
• Reduced polyp extension (PE): especially compared to the coral’s baseline behavior
• Color loss/dulling: not the usual clean “nutrient fade,” more like stressed patchiness
• Tissue recession around base/hidden areas: where you don’t normally look
Eggs (why they matter)
Egg clusters are often found:
• near the base
• in shaded areas
• on plug edges or rock right next to the coral
They can be hard to see unless you’re specifically looking for them with good lighting and patience.
Why AEFW feel “impossible”
Because they’re not a one-step pest. They have a lifecycle, and the lifecycle is what you have to interrupt consistently. That’s why prevention is so heavily emphasized among SPS keepers: it’s vastly easier than cleanup.
Final Thoughts
AEFW are not a casual nuisance — they’re a host-specific coral predator. If you’re building an Acropora collection, the real “skill” isn’t just alkalinity and lighting. It’s having the discipline to treat every new Acro like it might be carrying something.
The two outcomes in the hobby are very predictable:
• People who build strict intake habits rarely deal with AEFW long-term.
• People who skip intake habits eventually deal with AEFW.
Not because they’re unlucky — because AEFW travel through normal hobby behavior.