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Aquarium Pests: Montipora-Eating Nudibranchs

Growing…growing…gone.  Unfortunately, this is an all-too-common story in the reefkeeping hobby due to a pest aptly named for its favorite meal, the Montipora-Eating Nudibranch. 

Pink plating Montipora nearly gone from Montipora-Eating Nudibranchs

Montipora-Eating Nudibranchs (M.E.N. – just kidding, I won’t use that acronym) are from the phylum Mollusc, class Gastropod, sub-class Opisthobranchia, order Nudibranchia, and sub-order Aeolidoidea.  Identification down to the species level has not yet been accomplished to my knowledge.  They are white in color and range in size from 1-3mm in length.  The body is covered in cerata, which may store the nematocysts (stinging cells) of the coral to help protect them from predators.

Adult Montipora-Eating Nudibranch on the base of a Montipora Digitata

The key to detection is to understand the life cycle of these nudibranchs.  If there is one nudibranch, it is capable of reproducing asexually.  The adults lay tiny clusters of 3-20 eggs (Borneman, 2007) in crevices along the base of the coral.  As the eggs hatch, the juveniles immediately join the adults in eating the coral in a distinct jagged line along the base and edges.  Reportedly, these nudibranchs can survive extended periods with no food source. 

Treatment for the Montipora-Eating Nudibranchs comes in the forms of prevention, natural predators, and chemical destruction.  Prevention lies in purchasing from a reputable dealer or hobbyist first and foremost.  Chances are, if the person has had them before, he will have them again.  Next, the responsibility falls to the new owner of the coral in proper quarantine procedures (at least two months is recommended).  Examination with a magnifying glass is recommended to help identify and remove eggs; however, the nudibranchs might have laid eggs in a hidden crevice.  Since the eggs are laid at the base of the coral or on dead coral skeleton, some hobbyists chose to remove the coral from the base rock, and leave some coral left behind.  The base rock is then left to die.  This is to help ensure that the eggs are not transferred.  Additionally, dipping the coral in an iodine solution has shown to be effective in killing adult nudibranchs (but not the eggs).

Some hobbyists have found certain natural predators will help control the nudibranchs, but there are no known complete eradication measures available naturally.  The wrasses generally known to eat most invertebrates will most likely also feed on the nudibranchs.  It is important to keep in mind that as far as natural predators go, what works for one hobbyist may not work for another hobbyist, especially with wild creatures.

Montipora-Eating Nudibranchs in a CoralRx Dip at the 45 minute mark – alive and happy

The last method of eradication is by chemical means.  Many hobbyists have found that an hour-long dip in iodine will kill most adult nudibranchs.  However, this may cause undue stress to the host coral, especially if flow, pH, and temperature are not ideal in the dip.  Levamisole (a pig de-wormer available at farm supply stores), which is commonly used to treat Acropora Eating Flatworms, has been used in a similar manner to the iodine dip, but with a higher fatality rate to the host coral.  Levamisole paralyzes the nudibranchs so they can be removed more easily from the coral.  Garlic and freshwater dips have also been used with fatal results to the nudibranchs as well as usually to the coral.  The latest chemical method is potassium permanganate.  The dip (50mg/l for 30-90 minutes – Borneman, 2007) has been shown to effectively destroy both the adults and the egg masses with little impact to the coral.  After eradication on the corals, the main tank should be kept free of Montipora for approximately two months.

Like all chemicals, caution should be exercised when handling potassium permanganate.  Using an MSDS (Material Safety Data Sheet) to learn about the hazards of use and what protective gear is highly recommended.  An MSDS for potassium permanganate suggests the use of eye protection, gloves, and respiratory protection as potassium permanganate can cause serious burns to the skin, nose, and throat.     

Although there are still no full-tank chemical treatments, the eradication of the Montipora Eating Nudibranch is possible with patience and proper husbandry.  Currently, using a combination of quarantine and potassium permanganate seems to be the most effective against these pests.

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