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 (Phestilla subodiosus). Although treatment of Montipora-Eating Nudibranchs is historically challenging, this article covers several available options.
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. From there, they are of the suborder Aeolidina, superfamily Fionoidea, family Trinchesiidae, genus Phestilla, species subodiosus. Identification down to the species level was only accomplished as recently as 2021, although the hobby has been actively fighting them since at least the early 2000’s (Wang, et al., 2020).
How to Identify:
These nudibranchs 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. Shown in the picture is a single Montipora-Eating Nudibranch (circled in red) at the edge of a Montipora digitata coral.
The key to detection is to understand the life cycle of these nudibranchs. If there is only 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 (see image). 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.
Back in grad school, I modeled the lifecycle of these nudibranchs and how various treatments worked on them. Unfortunately, the results were never promising once the nudibranchs established themselves in a mature tank. (Note: Sadly, I built this model with an educational license, and my files are “legacy file types” for the software. I have been unable to regain access to my work for either historical purposes or additional research.)
Montipora-Eating Nudibranch Treatment Options:
Treatment for the Montipora-Eating Nudibranchs comes in the forms of prevention, natural predators, chemical destruction, and manual removal.
Treatment Method 1: Prevention of Montipora-Eating Nudibranchs:
Prevention lies in purchasing from a reputable dealer or hobbyist first and foremost. Chances are, if the person has had them before, that person 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. Both remaining coral on the rock and base rock then dies. This is to help ensure that the eggs are not transferred.
Treatment Method 2: Controls for Montipora-Eating Nudibranchs
Some hobbyists have found certain natural predators will help control the nudibranchs. Unfortunately 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.
Treatment Method 3: Coral Dips for Montipora Eating Nudibranchs
The last method of eradication is by chemical means. Coral dips often help stun the pests so they can be blown off gently with a pipette or powerhead. These adult Montipora-Eating Nudibranchs (as pictured) were in a dip much longer than the coral colony could survive. Unfortunately, that is typically the case; however, there are a few less lethal options.
Montipora-Eating Nudibranch Treatment: Iodine
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.
Montipora-Eating Nudibranch Treatment: Levamisole
Levamisole (a pig dewormer available at farm supply stores), 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.
Montipora-Eating Nudibranch Treatment: Potassium Permanganate
Another 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 moderate 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.
Montipora-Eating Nudibranch Treatment: Series of Dips + Manual Removal
Rather than trying to kill both adult nudibranchs and eggs, I attempt to just break the lifecycle by removing the adults so that they cannot reproduce. When I get any frags of Montipora, I perform my usual coral intake process. I perform an inspection, remove the plug/base/dead skeleton, perform dips with manual pest removal, and attach a new base. Then I place the coral into my quarantine tank, but it stays for an extended period (60 days rather than the typical 30 days).
Since a succession of coral dips work for AEFW and red bugs, I also dip all Montiporas daily the first week to aid in manual removal. After that, I dip every other day the second week, every third day the third week, and then once a week for weeks four through six. I have not lost a single coral with this method, and it saves me the hassle of treating with different medications for different parasites at different times.
Various dips may work to stun the nudibranchs, and examples include CoralRx, Revive, and Tropic Marin Pro Coral Cure. Again, here the goal is to simply aid manual removal by stunning the adults. If the adults are removed, the eggs will continue to hatch in the presence of food. Adults are then easily removed before they can reach maturation. In the lifecycle model mentioned above, this was the most successful approach when implemented correctly.
Montipora-Eating Nudibranch Treatment: Display Tank + Dips
The worst challenge is a display tank with mature colonies infested with nudibranchs. My best advice is to consider the coral dip series described above (although large colonies may require buckets for treatments). Additionally, the hobbyist would have to kill any bases left attached to the rock along with unremovable encrusted Montipora colonies. Another option, if the colonies are smaller, may be for the hobbyist to remove all Montipora from the display tank. The hobbyist would then place all removed Montipora into a quarantine tank for treatment, minus a sacrificial frag that stays in the display. The hobbyist must then frequently replace that sacrificial frag so as to draw out the nudibranchs from the rockwork.
Montipora-Eating Nudibranch Treatment: Other Dip Options
Hobbyists have used garlic and freshwater dips with nudibranch mortality but they also often report high coral mortality.
Conclusion:
Although there are still no full-tank chemical treatments, eradicating Montipora Eating Nudibranch is possible with patience and proper husbandry. Using a combination of dips and manual removal seems to be the most effective option available at this time.
