Acropora-Eating Flatworms (AEFW): How to Identify and Treat Them
- , by Mark Davis
- 4 min reading time
Acropora-eating flatworms are one of the most feared SPS pests in the reef hobby. Learn how to detect them early, treat effectively, and protect your Acropora colonies. Shop Healthy Corals at Reefverse Every coral at Reefverse is carefully inspected for health and quality. Browse our collections and build the reef of your dreams. 👉 Shop All Corals
What Are Acropora-Eating Flatworms?
Acropora-eating flatworms (Amakusaplana acroporae), commonly called AEFW, are a specialized reef pest that feeds exclusively on Acropora corals. They are widely considered one of the most destructive SPS pests in the hobby—capable of wiping out an entire Acropora collection if left untreated.
AEFW are exceptionally cryptic and often go unnoticed until significant damage has already occurred. Early detection, strict quarantine, and repeated treatment are essential to successfully eliminate them.
How to Identify Them
AEFW are masters of camouflage:
- Small (2–6 mm), flat, and nearly transparent with a tan to brown coloration that closely matches Acropora tissue
- Commonly found on the undersides of branches and near the base of colonies where they’re protected from light and flow
- Eggs appear as small white or cream-colored oval clusters cemented firmly to the coral skeleton
- Best detected by dipping the coral and inspecting the dip water under a flashlight or by examining the coral with a magnifying glass or jeweler’s loupe
Signs of an Infestation
- White bite marks or irregular patches of missing tissue on Acropora
- Reduced or absent polyp extension despite otherwise stable water parameters
- Slow tissue recession, often beginning on the underside or interior branches
- White egg clusters attached directly to exposed skeleton or frag plugs
- Flatworms visible in the dip container after the coral is agitated
Why They’re So Dangerous
AEFW feed directly on Acropora tissue and polyps, leaving behind characteristic feeding scars that weaken the coral over time. Heavy infestations can cause rapid tissue loss, poor coloration, reduced growth, and eventually death.
The greatest challenge is that their eggs are resistant to all commonly used coral dips. Because of this, even if every adult flatworm is killed, newly hatched worms can restart the infestation days later. Successful treatment requires repeated dips combined with manual egg removal over several weeks.
AEFW spread easily between Acropora colonies through direct contact, shared frag racks, contaminated equipment, and newly acquired frags.
Treatment
1. Coral Dipping (Primary Treatment)
Repeated coral dipping remains the most effective method for eliminating adult and juvenile AEFW.
Commonly used dips include:
- Revive Coral Cleaner
- CoralRx
- PolypLab Reef Primer
- Bayer Advanced Complete Insect Killer (historically popular but discontinued and no longer widely recommended due to changing formulations and safety concerns)
Dip Process:
- Prepare the dip according to the manufacturer’s instructions.
- Submerge the coral for the recommended amount of time.
- Use a turkey baster or pipette to blast every surface of the coral, paying special attention to the undersides of branches.
- Inspect the dip container for flatworms.
- Carefully scrape or scrub away every visible egg cluster using a soft toothbrush, dental pick, or scalpel.
- Rinse the coral in clean saltwater before returning it to quarantine.
Repeat every 5–7 days for 6–8 weeks to eliminate newly hatched flatworms before they reach maturity.
2. Biological Predators
Several wrasse species are known to consume adult AEFW that become dislodged during dipping or naturally move around the aquarium.
Common predators include:
- Melanurus Wrasse
- Six Line Wrasse
- Yellow “Coris” Wrasse (Halichoeres chrysus)
- Leopard Wrasses (Macropharyngodon spp.)
While these fish may help reduce populations, they will not eliminate an established infestation and should only be considered a supplemental control method.
3. Quarantine Treatment
For moderate to severe infestations, move all affected Acropora to a dedicated quarantine system.
This allows:
- Repeated dipping without disturbing your display aquarium
- Easier inspection for new bite marks and egg clusters
- Prevention of spreading AEFW to healthy Acropora
Continue treatment until no bite marks, worms, or egg clusters are observed for several consecutive weeks.
Prevention
- Dip every new Acropora before introducing it into quarantine.
- Quarantine all new SPS corals for 6–8 weeks, inspecting them regularly.
- Carefully inspect frag plugs, exposed skeleton, and branch bases for egg clusters.
- Avoid sharing tools, frag racks, or water between quarantine and display systems.
- Remember that coral dips kill adult flatworms but do not kill eggs, making quarantine your best defense.
Key Takeaways
- AEFW are one of the most destructive pests affecting Acropora corals.
- Their eggs are resistant to coral dips, making repeated treatment and manual egg removal essential.
- Repeated dipping every 5–7 days for 6–8 weeks offers the highest chance of complete eradication.
- Wrasses can help reduce populations but should never be relied upon as the sole treatment.
- Prevention through quarantine, inspection, and coral dipping is far easier than eliminating an established infestation.