Blue Steel Zoanthids
Zoanthus Coral Care
Zoanthus and Palythoa are a large group of corals in the reef keeping hobby. They come in an incredible range of colors and patterns making them very popular with both beginner hobbyists and rare coral collectors tracking down uncommon color morphs. In terms of care, both Zoanthus and Palythoa are fairly easy to keep. They tolerate a wide range of lighting intensities and water conditions. Once settled in, zoas multiply quickly. Please see below for more care tips for Zoas and Palys as well as checking out our Top 5 Tips for setting up a reef.
Zoanthid Taxonomy and Identification
Zoanthus are a genus of corals within the order Zoantharia, an order it shares with Palythoa and Parazoanthus. You may have also heard zoanthus referred to as zoanthids which is correct, but if you want to be a stickler for details, the term zoanthids refers to all the corals in the order while zoanthus is specific to the genus.
There is quite a lot of active research on Zoanthid taxonomy and the cutting edge is DNA classification. It is not nearly as straight forward as it may seem. There is a LOT of genetic consistency so it is a chore to find small segments of DNA that are actually different enough to base a scientific classification on. Over 90% of the coral’s genome is identical so a lot of current research is delving into that. Genetic research is further complicated by the effect the environment has on the expression of the genetic code. The genes themselves don’t change but the how the organism reads the genetic code in response to the environment does so you could see two very different traits in corals originate from an identical genetic sequence. I expect quite a lot of reclassification to occur in this space.
What was once 300 identified species has been whittled down to around 50-60 in the past several years depending on the criteria used to differentiate the different morphs. There are new classification insights as more genetic testing is being done, but for the purposes of this hobby-focused website, we've chosen to arbitrarily lump larger polyp individuals into Palythoa and smaller polyp specimens into Zoanthus.
As a practical matter, there is some degree of fogginess you will encounter in this industry whether something is called a Zoanthus or a Palythoa because there is a wide range of physical variation within the genus. On the far ends of the spectrum the two are easy to differentiate but once you get into large polyp Zoanthus variants and smaller polyp Palythoa variants, the naming convention breaks down at the hobbyist level.
Before we get into the care tips for zoas, I need to address the potential toxicity of these corals. Some can contain a compound called palytoxin that is a very dangerous poison. Palytoxin is associated more with Palythoa than Zoanthus, but it is possible for zoas to have it. I don’t know if those zoas produce it themselves or acquire it from neighboring Palythoa. In the wild, palytoxin shows up in organisms that don’t actively produce it such as sponges, mussels, and starfish but live in close proximity to palythoa. It can even be found in other species up the food chain such as crabs and fish through biomagnification. I’ll touch on this again when we discuss pests, because as lethal as palytoxin is, there is no shortage of organisms that are more than happy to consume them with no ill effects.
The scientific community has been aware of palytoxin since the 1960’s but it has been used as a means of biological warfare by Polynesian cultures for much longer. There is a legend of a sacred seaweed that grew in a special pool that when applied to a warrior’s spear would bring sure death to his enemies. In 1961 researchers tracked down the fabled pool in Maui and found colonies of Palythoa toxica.
It wasn’t until the 1990’s that the mechanism of action was identified. Palytoxin binds to the sodium potassium pump on the membrane of cells. If you don’t remember what this is from high school biology, the sodium potassium pump is REALLY important to ion movement in and out of the cell and affects all sorts of biological processes so any interruption of that royally screws things up. It is why the symptoms of palytoxin poisoning are seemingly all-inclusive. Initially there was some skepticism regarding this mechanism of action but it was confirmed in 1995 in a pretty clever study. They exposed yeast cells to palytoxin because yeast cells don’t have a sodium potassium pump. Those yeast cells were unaffected but when given to yeast cells that researchers genetically modified to encode a sheep’s sodium potassium pump, all the cells died.
In practice you are not likely to get palytoxin poisoning just by having zoas or palythoa in your home aquarium. It resides in the flesh of the coral so it becomes an issue when the colony is damaged. People have gotten sick from scrubbing palythoa off of rocks or propagating a colony with a band saw that would send the particles airborne and then inhaled. People have also gotten sick by boiling rocks with colonies on it because that too sends the compounds airborne and unlike many other proteins, palytoxin does not lose its toxicity when heated.
Zoanthus and Palythoa are found in corals reefs around the world. These polyps are harvested mainly from the islands of the Indopacific including Fiji, Tonga, Solomon Islands, and the Great Barrier Reef. Zoanthus and Palythoa have an incredible array of colors and patterns that make them one of the most popular corals in the reef aquarium hobby.
Zoanthus and Palythoa are not as demanding as other corals when it comes to lighting. They can be kept under a wide variety of lighting types, and are tolerant of both low and high light conditions. It is always wise however to acclimate new arrivals in lower light areas because it is far more likely to be damaged from overexposure than starve from underexposure.Low Light
Low light translates to about 30-50 PAR
Medium Light is between 50-150 PAR
High Light is anything over 150 PAR
Lighting is a loaded topic, so for a more in-depth discussion of lighting, please see our Deep Dive article.
Zoanthus by their very shape invite detritus accumulation and a zoa colony that is dirty is very different than one that is kept clean. The buildup of detritus can slow a colony’s growth or even cause it to die back.
Strong water flow helps keep detritus buildup to a minimum as well as flushing away waste that the colony generates.
When designing flow patterns for this coral I like to provide strong consistent flow with short bursts of very strong flow. If you do jot have controllable pumps to achieve this it can be done manually with a turkey baster. Once a day you can squirt water at the colony to dislodge any buildup. I use just enough force to close the polyps up.
If you decide to go this route only do this with established colonies that are well attached. If you have a freshly glued frag of zoas they might get blown away.
While both Zoanthus and Palythoa polyps derive much of their energy from the products of their zooxanthellae, they do have the ability to capture prey. Palythoa seem to feed much more readily than their Zoanthus counterparts.
We try to feed a blend of small frozen foods such as the fines from mysis shrimp, cyclops plankton, and frozen rotifers. We have also tried feeding a variety of powdered dry plankton. Your mileage may vary depending on the species of zoa you have and also how you are doing the feeding. As I mentioned they are not nearly as good a feeder as palythoa so they might not be able to grab chunks of food out of the water. I try to turn the pumps off and then give them a good dusting of food and let them sit for about 10 min before restarting the pumps. Take a look at the feeding video below.
Both Zoas and Palys for the most part have been propagated extensively in captivity and are an excellent candidate for aquaculture. It is reasonable to believe that a sustainable harvest can be achieved in time. Take a look at the propagation video below for tips on how to frag Palythoa and Zoanthus.
Proper acclimation is extremely important considering the stress imposed on the animals by the shipping process. Please take a moment to review our Acclimation Guide.
The images were taken with a Canon 5Ds R and 100mm macro lens. The lighting we shoot under varies depending on the tank. At this time T5 produce the best results. Quite a lot goes into how we go about shooting the corals and anemones you see on Tidal Gardens. For an in-depth look at our methods, check out our comprehensive Reef Aquarium Photography FAQ.