Nudibranches – The Good, the Bad, and the Ugly

Cory here. I thought I’d take my next few blogs to go over the “ins and outs” of Nudibranches. Like lots of organisms living in an aquatic system, these interesting creatures bring a host of features to your saltwater tank. And, along with the good, it’s important to point out the bad…and the down right ugly things about nubibranches in your aquarium too.

The Bad:

Nudibranches target Montipora, Zoanthids, and Softies

There are so many coral eating organisms, Butterflies and Angelfish are the obvious ones. However, some of the worst pests are ones that you can barely see. Flatworms and Red bugs are most notorious for destroying Acropora species. However, Montipora species have their own pest: a Nudibranch.

They are hard to see, especially if you do not know what you are looking for. The largest I have seen was a half centimeter in length, tucked behind a crevice in the coral. They are always near a piece of the coral that is in the process of dying. This particular nudibranch feeds only on Montipora tissues, more commonly the plating varieties such as Montipora capricornis. They lay their eggs in a spiral or cluster, on the underside of the coral. Usually hatching within a few days, depending on water conditions, they immediately begin munching on the coral tissue. A couple adult Nudibranches can easily consume a one inch frag in 24 hours.

There isn’t a simple way to eradicate them. Dipping the corals in a Lugols Iodine or Tropic Marin Pro Coral Cure solution will help to loosen the nudibranches, so they can be extracted. The dip however, will not kill the egg mass. The eggs must be removed immediately using a scraper, toothpick, or a toothbrush. Any portion of the coral that has died or seems to be infected should be cut off just in case there are eggs imbedded in the skeleton.

Nudibranches are also commonly found feasting on Zoanthid polyps. These particular types of Nudibranches are especially hard to find because they look very much like the polyp that they are eating, even matching the color in most cases. Zoanthids commonly close and stay closed for days, eventually polyps begin to disappear. This is usually the first sign of infection. Again, like the Montipora Nudibranches, dips will only remove the adults, leaving the eggs behind. The eggs are usually laid on the underside of the poylps, but can also be found on the rock itself.

Soft corals have many different species of Nudibranches that prey on their tissues. Some are extremely large and colorful, while others camouflage themselves, making detection extremely difficult. Like other corals, removing the adults with coral dips and manually removing the eggs when possible is the only effective way.

There are so many species of Nudibranches in the oceans, many found on the Reef and serving some purpose good or bad. We are learning more each and everyday about Nudibranches, what they eat and where they come from. We are importing corals from around the world, in some cases from areas we have never collected before. With new locations, comes new pests and most likely new Nudibranch species, good and bad.

Check back soon for the next part of this article.

Happy Thanksgiving!

Cory