One of the most difficult pests to fully eradicate in most reef systems are the Zoanthid-eating nudibranch. With their uncanny ability to hitchhike into the tank in nearly any coral colony, and to spread into plague proportions at record speed, they have fully established their reputation as a pest that cannot be taken lightly. Over the years, several methods for treating these pests have emerged, from freshwater iodine dips to manual removal, but all of these methods seemed to extremely stress the zoanthid colonies as well. Zoanthids were being lost during dips, they became much more susceptible to fungus, and a new method had yet to emerge.
I had initially set out to remove another pest: a large mass of flatworms that were on a colony of zoanthids. The red flatworms had reproduced to the point that they were completely drowning out the zoanthids, and the colony had been closed for nearly a week. I placed 8 drops of Salifert’s Flatworm Exit (FWE), an excellent flatworm treatment medication, into 3 gallons of tank water in a bucket.
After 10 minutes, I removed the zoanthids colony, and noted that all of the flatworms were dead at the bottom of the bucket. Much more interestingly, however, I noticed that there were a few zoanthids eating nudibranchs that were also at the bottom of the bucket, whether alive or dead it was hard to tell, but they had certainly been removed from the colony. Immediately curious, I collected some nudibranch from a colony of zoanthids that was still acclimating and waiting to be dipped in iodine and freshwater for nudibranch removal.
The nudis were placed into two containers, one containing a test group and one a control group.
Each container contained two cups of water from the tank. Into one, there was added 4 drops of Salifert’s FWE. Nothing was added into the control group in order to monitor the effects of the FWE versus nothing at all.
I had initially created a control group because I expected that this experiment would run its course during several hours, possibly days, and that it may or may not have worked. I had no idea how amazing the results would be, or how quickly they would happen.
In 30 seconds, one of the nudis in the test cup was falling from the side of the cup. In 45 seconds it looked like this:
The results were fast, effective, and much, much less stressful for the zoanthids colonies than the freshwater iodine dip.
The control group showed no ill effects during this time. Obviously, the control group was not going to be “released into the wild,” so I attempted to repeat the experiment by adding 4 drops of FWE since they were in better locations for pictures.
This treatment certainly seems to work wonders against zoanthid eating nudibranchs. In fact, Salifert’s FWE proved to be completely safe for zoanthids colonies, it did not stress them at all! It is the only discovered treatment for zoanthids that not only has a 100% death rate for the nudibranch, but will also leave the zoanthids entirely unaffected.
Not only is FWE safe for your zoanthids, it is also reef safe! This means that if you have an infestation in your entire tank, you can now treat with a heavy dose of FWE and get all of the nudibranch, then retreat every week to deal with the newly hatched eggs for three weeks. Finally, a new treatment which is safe, very effective, and extremely easy for ridding your system of zoanthid eating nudibranch once and for all.
As always though, care is required, since 4 drops per 2-4 cups is nearly 4 times the recommended dosage, and is much easier (and much cheaper) to carry out in a bucket than in an entire system. Since this dipping system works with your regular tank water, you can leave the colonies in the bucket for nearly 30 minutes to several hours with no ill effects. They can then be placed into a bucket of only tank water for 10-30 minutes in order to remove any FWE that may still be on the colony, and placed back into the tank or quarantine system.
This method is also very much recommended for new colonies being introduced into your tank to avoid any further infestations. After being dipped in FWE, the colonies should be closely visually inspected for nudibranch eggs, which are not affected by FWE. The eggs are not difficult to find, they are approximately a ¼”, thin strand of very bright white eggs. Remove them with a pair of tweezers, give the colony a good shake in the bucket water to clear any residue of the eggs, and then place the colony into your quarantine system. If you do not have a quarantine system then you may want to consider one to avoid any future infestations, otherwise the colony can be placed into your main system as long as it is very carefully monitored for a few days.
I hope that this pictorial has helped you as much as it has me, and that you can appreciate the beauty of your zoanthids without letting them ever become food again!