Aquarium Pests: Acropora-Eating Flatworms (AEFW)

After purchasing yet another coral infested with Acropora-Eating Flatworms (AEFW) from a local aquarist, I decided an article on how to treat these nasties was long overdue. 

AEFW have flooded the reefkeeping community in the last few years, and unfortunately many aquarists are choosing to just live with them or get out of SPS-keeping entirely.  As aptly named, AEFW only feed on Acropora sp. corals and are rarely (if ever) found on anything else.  These flatworms are teeny (few millimeters) and are able to blend in completely with the coral by digesting the coral’s zooxanthallae.  Typical red planaria flatworm treatments, such as Salifert’s Flatworm Exit, have absolutely no effect, except at extremely high concentrations over 30x the recommended doseage (and that’s just cost prohibitive).   

In March 2011, the AEFW were officially named Amakusaplana acroporae in a study published in Coral Reefs.  That study found that each adult can lay several egg batches, with each batch containing 20-26 egg capsules, and each capsule containing 3-7 embryos.  If you do the math, that’s about 180 flatworms minimum.  On the more devestating end of the scale, each adult could produce more than 700 offspring.  (Insert heebie jeebie dance here!)  Embryonic development takes 21 days.  I highly recommend quarantine and treatment prior to introducing corals into the display aquarium. 

How to Identify:
Identifying AEFW located on an Acropora while the coral is still in the aquarium is next to impossible.  These flatworms have excellent camouflage by using the coral’s own zooxanthallae.  The best identification method is by the small white bite marks, typically on the underside of the coral.

Update 2/23/2012:  Unfortunately I now have my own AEFW egg photo.  Eggs are typically located on dead coral skeleton or on/near the frag plug/base rock.  The were on the underside of an infested Acropora frag plug.
How to Treat:
At this time there is no in-tank treatment that is 100% effective, and supposed 100% effective treatments aren’t always 100%.  This is why I stress quarantine so much.  Once AEFW are in a display aquarium, there are no good options. 
Method 1:  Control
AEFW can be controlled through the use of various fish (wrasses, mandarins, etc.)  Each week all Acropora corals must be blown off with a turkey baster or a soft powerhead.  The AEFW will be blown off the coral into the water column so that fish can eat them.  This method is not 100% effective as some adults survive and all eggs are unharmed.  Additionally, one study I read (and I cannot remember the source or I’d cite it here) found that wrasses do not actually eat the flatworms.  They simply chew them up and spit them out.  According to an article by the Birch Aquarium, a piece of a flatworm containing some brain tissue can regenerate asexually.  Therefore, “natural” control methods are nowhere near 100%.  I advise against this method for people who travel (and therefore cannot do this weekly) or for people who intend to sell/trade their corals. 
Method 2:   Fluke Tabs
This is a simple, effective method, and it is fairly safe for corals (but the corals must still be treated outside the aquarium). Use 1 tab per gallon (or 4 tabs per 5 gallons) and dip the coral for 20-25 minutes. Repeat weekly for 6-8 weeks.
Method 3:  Coral Dips (CoralRx, Lugols, TMPCC, etc)
A single coral dip will remove and sometimes kill the adults with little harm to the coral.  Enough dips over a long enough time will kill the adults before they can reproduce.  Various coral dips work, but I prefer to use CoralRx and follow manufacturer’s instructions.  However, I need to point out that in my experience, CoralRx is too harsh on smooth-skinned Acropora corals (such as A. echinata, A. turaki, etc.)  Therefore, I use Lugol’s iodine for those Acroporas.  In the first week, I dip each Acropora coral separately every single day.  The second week I dip each coral separately every two days.  In the third week, it’s every three days.  I continue that pattern for 6 weeks (remember embryonic development takes 21 days).  This is a good option for aquarists who do not have a hospital tank as the corals can be returned to the main tank immediately after dipping.  I use a hospital tank to help ensure success since AEFW will starve to death in ~5 days in the main tank. 
Method 4:  Betadine
Betadine is used as an antiseptic and can be found at a local pharmacy.  Use 3 ml per litre of water and dip for 25 minutes.  Although this method kills the AEFW, it is also believed to kill beneficial bacteria on the coral.  After dipping, the coral is usually “browned out” and takes several weeks to recover.  I have not used this method because the coral dips and Fluke Tabs work better in my opinion.
Method 5: Levamisole
Levamisole is a pig de-wormer found at farm supply stores. To treat the Acropora corals, they must be removed entirely from the display aquarium and treated in a hospital tank. Losses from this treatment are estimated at 20-60%, so I have personally not used this method. This method is generally considered “not worth it” in the reefkeeping community.
Method 6:  Fresh Water Dips
Fresh water dips work to some extent, but they are rather difficult to perform (pH and temperature must be the same as the aquarium water) and are typically harsh on the coral.  I do not recommend this method.
Methods that don’t work:
Acropora crabs, flatworm-eating nudibranchs, Interceptor 
Last Note:  Ethics
I can’t end this article without a note on ethics.  If you have AEFW or any other known pest, please be a responsible reefkeeper by disclosing that information to potential recipients of your corals.  Selling/trading infested corals helps no one, including yourself.  Telling someone you have a pest does not necessarily mean that person won’t buy your coral, but it does allow them to make an informed purchasing decision. 
Rawlinson, et al, “Taxonomy and life history of the Acorpora-eating flatworm Amukusaplana acroporae nov. sp.”, Coral Reefs, March 2011.
Nostratpour, Ferdinando, “Observations of a polyclas flatworm affecting acroporid corals in captivity”, Advances in Coral Husbandry in Public Aquariums, 2008.  http://www.burgerszoo.eu/media/108785/chapter%206.pdf
Levenson, Mark, “My Own AEFW (Acro Eating Flatworm) Images”, ReefCentral, 2006.

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