Revisited: The Montipora Eating Nudibranch

Aquarium Pests: The MontiporaEating Nudibranch / Aeolid Nudibranchs

Introduction to the Montipora Eating Nudibranch

One of the more common and serious pests that have become an increasing issue is a species of nudibranch (or perhaps multiple species) known to feed on the tissue of corals from the Montipora and Anacropora genus. These nudibranchs can cause massive amounts of damage to coral in a very short amount of time. They are biologically designed to multiply at an astounding rate in an effort to compete with their constant predation in the wild. It is with no surprise that when you toss them into an environment with few if no predators, such as most home aquaria, these Nudibranchs thrive and are one of the many pests that aquarist keeping stony corals should be aware of.

A close up of a nudibranch found feeding on the tissue of a colony of Montipora spongodes. You can clearly see the cerata in which the nudibranch stores the nematocysts of its ingested prey.

Hosting Behavior on Montipora Species Description

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.

As the nudibranchs feed, they typically start at the base of the coral, or a bare spot within or near a crevice. From there, they start to feed on the edge between the fresh tissue and newly exposed skeleton and slowly work their way away from the starting point. They typically feed directly at the border of fresh tissue, however when there are many other nudibranchs present and there is a lot of competition for the food, the nudibranchs will become much more mobile and move beyond the border to feed.

Once the original food source is fully consumed (and often before), the nudibranchs will search for an alternate source and spread throughout the tank. It is not yet known how long the nudibranchs can survive without a host coral present but there have been several cases of them surviving in a tank for over two months without any Montipora.

Description

The nudibranchs themselves are typically small and rarely exceed of a centimeter 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. These cerata have a unique defense mechanism utilizing the stinging cells from their victimized coral to use for their own defense. These stinging cells are called nematocysts and after being ingested by the nudibranch they are transported and stored in the very tips of the cerata. The nematocysts serve to protect the nudibranch from potential predators by deterring them from being consumed. Since Aeolidoidea nudibranchs breathe through their skin, the cerata also aid in respiration by increasing the surface area of the skin.

The habits of the nudibranch give the impression that they are asexual, not needing another nudibranch in order to lay eggs. A single adult can lay over 100 eggs and once the eggs have been deposited on or around the host coral they only take a few days to hatch as they have already been incubating within the adult before being laid. 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.

These pictures (above) show what an egg laying adult and egg masses look like. On the right is a key as to what is in the picture on the left. There are also many other eggs and adults not circled in the picture.

Treatment Options

1. Chemical baths(dipping): These options offer different ways to kill the adult specimens of nudibranchs. Eggs are unfortunately resistant to these treatments however it may reduce the successful hatch rate. Eggs must be either removed manually, if they can be found, or allowed to hatch to be treated as adults. 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 all 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.
   1. Iodine/derivatives (ex. lugols iodine, Tropic Marin pro-coral cure, Seachem reef dip) when used at recommended dosages and times, these medications 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.
   2. Another option for chemical baths is Levamisole, a drug created to treat worm infestations in animals. It acts as a contact poison blocking nerve transmission to kill or stun the parasite. 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 paralyzed and fall off the coral. This treatment can be used in an existing reef system, however it is advised that it be administered in a separate tank, as there can be a lot of secondary die off of aquatic life. Note, Levamisole is only available with a prescription from a licensed Veterinarian.
   3. Freshwater dipping is a very dangerous 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. Note, this is not recommended as a safe treatment option as it can be very harmful to the zooxanthellae in the coral, longer exposure times can and will kill coral.
2. 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. Nudibranchs can either be scooped up with tweezers but scraping/squishing their body with a toothpick will also work. 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.
3. Introduction of natural predators: Fish such as certain members of the Pseudocheilinus (Sixline wrasses), Coris (Coris wrasses), and certain Thalassoma (Banana wrasses) Genus 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. There are many other natural predators,including certain crabs, several other nudibranchs, and perhaps more, however these are not as commonly available to the aquarist as the aforementioned fish.

These pictures (above) show how much damage these pests cause and how quickly they can reach plague proportions. Only 7 days before the picture on the left there were no adults and no damage to be found on this coral, eggs at that time were also unable to be found. The picture on the right shows what the coral looked like 4 days after the first picture was taken.

Preventative Measures

1. Quarantine all corals, not just Montipora. These nudibranchs will actively travel around to look for additional hosts. This behavior has led to the introduction of nudibranchs to aquaria through additions of coral or rock other than Montipora. One must not assume that if no Montipora are being introduced to a tank, then there is no possibility of introducing these nudibranchs. It is not known how long their adult life cycle lasts, however there have been reports that these nudibranchs can last several months without a host coral present. Therefore it would be prudent to maximize the amount of time coral and live rock stay in a quarantine system.
2. 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.
3. Dont assume that if your supplier seems like a knowledgeable person and always has good quality corals that they may not have these nudibranchs. Treat all corals as if they are infected and properly quarantine each new specimen.

A close-up of three egg laying adults (lower left and lower center) with alarge mass of eggs (center). The eggs are laid in multiple clusters of what appears to be between 10-30 individual eggs per cluster.

How can stores protect themselves from becoming infested with these nudibranchs?

1. Much like the recommendations for hobbyists, retail locations should incorporate quarantine processes for safeguarding their other corals. All incoming corals should be placed in a holding area where they can be monitored for pests and be allowed to recover from any stress caused by transportation.
2. Pay attention to the origin of corals with pests. It is likely that if they had them once, they will most likely have other corals with pests. Make an effort not to buy these specific corals from that vendor in the future and find an alternate source to supply you with that specific coral.
3. Employ a team of natural predators in any Montipora or Anacropora holding tanks. These will serve as a second pair of eyes to continuously search for and eliminate any unwelcome nudibranchs.