Montipora Eating Nudibranchs are serious pests and can cause massive amounts of damage to the tissue of corals from the Montipora and Anacropora genus. Unfortunately for the hobbyist, these nudibranchs multiply at an astounding rate. In nature this rate of reproduction is equally opposed by large scale predation, however, in the aquarium these predators often do not exist.
Hosting Behaviour on Montipora
The Montipora eating nudibranchs naturally prefer to host in corals with ample hiding spaces. Plating Montipora species such as M. capricornis seem to be a favorite as the whirling growth forms of the coral provides numerous crevices where the Nudibranchs can take refuge. Massive encrusting Montipora, however, seem to be less popular as most colonies are smooth and lack the crevices in which the Nudibranchs prefer to hide.
The nudibranchs themselves are typically small and rarely exceed a centimetre in length. Similar to most other members in the Aeolidoidea family they have two or more rows of frilly extensions called cerata which line the entire length of their back.
Nudibranchs are asexual, meaning that both sexes do not have to be present in order for offspring to be produced. A single adult can lay over 100 eggs, which only take a few days to hatch. The larvae start out very small, but within the first few days with an abundant food source present they grow quickly, reaching adult size in less than a week after hatching.
There are numerous ways of killing adult nudibranchs, unfortunately the eggs are resistant to these treatments and the best that can be hoped for is a lowered hatch rate. Eggs must be either removed manually or allowed to hatch and then treated accordingly. The key is to eradicate any adults before they get a chance to lay eggs. It is also best to dip all Montipora and Anacropora at the same time as well as rocks in close proximity to the infected corals, as the nudibranchs are known to frequently roam around in search of new host coral.
Iodine and its derivatives when used at recommended dosages will kill most, if not all, adults. Throughout the procedure it is important to stir the coral in an effort to detach any adults from the coral. Once the dip is complete, the coral should be inspected for any nudibranch remnants which can be removed using a toothpick.
Another option is Levamisole, a drug created to treat worm infestations in animals. This drug has proven to be a very effective treatment for both parasitic nudibranchs and flatworms. We recommend a minimum dosage of 50ppm for a total duration of 10 hours or more. At this dosage the nudibranchs become paralysed and fall off the coral. This treatment can be used in an existing reef system, however, ideally it should be administered in a separate tank, as there can be a lot of secondary die off of aquatic life. You may need a prescription to purchase this product.
Freshwater dipping is a very risky yet very effective treatment option. Freshwater creates a large difference in osmotic pressure between the inside and outside of the body of the nudibranchs. This sudden change in osmotic pressure causes the cells to rupture and quickly kills the nudibranch. The dip must be done with de-chlorinated water adjusted to the pH and temperature of the tank and must last no longer than 15 seconds. It must be noted that this is a risky treatment option, as it can be very harmful to the zooxanthellae in the coral. Exposure times longer than the recommended 15 seconds can and will kill coral.
Manual removal of adults and egg masses:
This method is very effective for aquarists with smaller colonies and the ability to remove those colonies/fragments from the water. Colonies with deep inaccessible crevices may need to be broken apart in order to provide access to all areas of the coral. With good eyes and careful observance, these pests can be eradicated within a matter of weeks, as their egg cycle time is less than a couple weeks in length. You can use a pair of tweezers or a tooth pick to pick off and/or squash the nudibranchs. Just be sure to either shake the dead nudibranchs off in a separate container of water or use a jet of water from a pipette or baster to remove any remaining parts.
Introduction of natural predators:
Certain fish species of the genus, Pseudocheilinus (Six line wrasses), Coris (Coris wrasses) and certain Thalassoma (Banana wrasses) are known to actively feed on these nudibranchs. While this can be an effective control mechanism, it may not completely get rid of all nudibranchs. Most of these wrasses lack the mobility to get to most of the places where the nudibranchs hide.
Quarantining all new corals is by far the best way to avoid introducing these pests into your aquarium. One must not assume that corals besides montipora will not contain these nudibranchs, as it is possible for nudibranchs to attach themselves to corals other than montipora. Therefore, it would be wise to quarantine all new corals.
Visually inspect each coral during selection and again before placing in your system. Any areas of freshly exposed skeleton on Montipora should be checked very thoroughly as this is a good indication that nudibranchs may be present. During the daylight hours, the Montipora eating nudibranchs are most commonly found in crevices and areas where they are safe from potential predators, so be sure to be very thorough in checking these areas. Also be sure to look for any egg masses especially in the crevices.