Zoanthid Eating Nudibranchs: Beautiful Killers.

Zoanthid-eating nudibranchs are a type of nudibranch classified as an Aeolidiidae, first described in 1797. All Aeolids survive by consuming cnidarians and their flesh utilizing serrated, radular teeth.

There are countless species which we encounter in home aquaria, and while they are rarely spoken of on the species level, aquarists describe them based on the type of cnidarian that they afflict in the aquarium. Montipora eating Nudibranchs (MEN), Zoanthid eating Nudibranchs (ZEN) and aiptasia eating nudibranchs are all commonly encountered by the average aquarist.

While beautiful, and sometimes utilitarian in the case of Berghia verrucicornis or as they are now known,  Aeolidiella stephanieae – Aeolid’s are not something that we want in our aquarium. In most cases the lifecycle of the species is short and simple enough that it can begin, end, and repeat in our home aquaria without the intervention of the aquarist. Some Aeolids (ZEN) in particular are believed to be asexual or hermaphroditic; which can cause quite the headache for the afflicted aquarium.

LifeCycle

ZEN’s lay egg masses on both the colony themselves, and on nearby rockwork. The egg masses are very tiny, which can make identification and discovery rather difficult. The Aquarist must assume if they see one nudi, they have dozens more.

When they are born, ZEN’s are brown in color, and not particularly
attractive as other nudibranchs in the wild.

As the ZEN’s locate and predate on the preferred species of Zoa, the pigment’s from the zooxanthellae, including any bio-luminecest pigments are visible in the nudibranchs coloration. This trait serves 2 purposes. 1 – Camouflage from would-be predators, and 2 – a warning sign to said predators that they are poisonous!

ZEN’s only eat Zoanthids. They do not consume Palythoa, or Protopalythoa. This has provided the occasional reefkeeper with an “easy out” – they simply stopped keeping Zoanthids and stuck with the other 2 mentioned species to alleviate the stress of the predators

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Eradication and control

There are several different methods that can be utilized to control an infestation. First will we discuss what to do when you encounter these pests.

As the nudibranchs will develop pigment that matches the zoanthid that they are predating, it can be very difficult to see something that is several cm’s long. In my experience, the best way to detect the Aeolids is to utilize a flashlight, or actinic bulb sometime during your normal “dark” cycle, as polyps may not be open for feeding. Depending on how many colonies  are affected you may need an additional set of eyes to spot them. They move quickly so if you are lucky enough to discover one have your tweezers (and rubber gloves) ready! Shine the light on your suspected colonies and fan the polyps with your hand to induce the retraction of the skirt, the nudis should become much easier to see. Physically remove all of the adult specimens you find. They make wonderful macro-photo subjects, so try not crush them!

A beautiful Aeolid in the authors aquarium (Beauty is in the eye of the beholder!)

If you’ve discovered adults, you can assume you have a full blown infestation which will require chemical treatment to eradicate. Malachite Green is an easy to source, cheap and effective dip to remove both the adults, and damage the egg mass. Other commonly available dips like ProCoral Cure,  ReVive coral cleaner,   CoralRX, and Flatworm Exit are also beneficial in the toolbox of the Nudi Killer.

Lugol’s solution has been used with varying degrees of success at a rate of 40 drops per gallon of RO/DI water. A ten minute dip will prove fatal for all soft-bodied pests and some snails, but will not affect the egg mass, so it must be repeated. I personally would avoid doing a fresh water dip for treatment to prevent further stress of the coral and mortality risks involved.

The Authors Colony before infestation

It is advisable, if at all possible, to quarantine all affected colonies immediately after discovery so you can treat the entire population at once.  Salifert Flatworm Exit in the QT tank will take care of the ZEN’s, but again, will also not affect the egg mass. One drop per gallon with no other chemicals/UV/ozone in the QT tank, with a follow up application 2-3 times, every 7-10 days should give the aquarist the piece of mind that they are looking for. The aquarist should be aware that when dosing FWE, you should be prepared to syphon out any visible die off as levels may rise rapidly and in turn cause further issues for the corals in QT.  Special care should be taken if FWE is utilized in the display aquarium (I do NOT advise this and it will not be covered in this article).

The QT process will also allow the aquarist to monitor the colonies for the presence of “Zoa-Pox”, which will be covered in a future column of Reef Notes.                                                                                                                                                            After infestation

Natural Predators
 

Natural predators for Aeolid’s include Wrasses in the genus Halichoeres (the Yellow Coris is my pick here) and Chaetodon Butterflyfish – which isn’t something most would ever want to risk in the common reef aquarium. I feel that natural predation is the least effective and
possibly dangerous as they will only consume the adult specimens, and not the egg mass. The Aeolids may continue to fly under the radar while your prized designer collection of “Dolce and Gabana – Garbanzo-Bean-People-Eaters” that you spent $30 a polyp for (again, another topic that will be covered in the future) are slowly wasting away.

Prevention

The number one way to avoid this problem is to Dip/QT/observe ALL incoming livestock for a period of 7 to 14 days. Prophylactic dips are also gaining popularity in the hobbyist circle, and for good reason. An ounce of prevention equals a gallon of cure. This has never been more true. As a responsible aquarist, it is our responsibility to notify others that we may be trading with of past and current infestations so that they can prevent passing these critters to one another.

 This is your Reef, take Notes!

Please feel free to ask questions in the comments or in the ReefNotes Forum