Zoanthids – corals for beginners

Zoanthids, soft corals belonging to the subclass Hexacorallia, are often referred to as zoas. While the descriptor “soft” leans more towards aquarium jargon than scientific taxonomy, it aptly captures their characteristic lack of a limestone skeleton. Nonetheless, despite this absence, Zoanthids develop a dense and relatively firm polyp tissue, distinguishing them from other well-known soft corals such as Xenia sp. The genus Zoanthus presents itself as an excellent option for novice marine aquarists, yet it also offers challenges that can engage even experienced hobbyists.


While taxonomically Zoanthus typically denotes a specific genus within the Zoanthidae family, it’s common among aquarists to employ it more broadly to encompass all corals resembling it within the Zoantharia order, including parazoanthus and palythoa. For consistency, I’ll maintain this convention throughout this text, acknowledging its simplification.

Speaking of taxonomy, during my research for this material, I encountered assertions suggesting that Zoanthids are not technically corals. I don’t intend to delve too deeply into this tangential issue, recognizing the inherently disputable nature of taxonomic classification. What was once categorized as a plant may not hold that classification today. I distinctly recall the educational shift from labeling bacteria as the simplest plants to recognizing them as animals during my primary schooling days. Many taxonomic schemes currently categorize the Zoantharia order as both Cnidarians and Anthozoa corals. While such classifications may evolve in the coming years, at present, I see no issue in referring to Zoanthids as corals.

What do Zoanthids look like?

The majority of Zoanthids tend to develop into colonies where each polyp maintains independence. In certain species, polyps may arise from a shared tissue known as Coenenchyme or, less commonly, through stolons. Typically, Zoanthids exhibit a small cylindrical polyp structure, anchored to the substrate on one end while culminating in a vibrant and distinct oral disc, encircled by tentacle-like arms.

Zoanthids present as small polyps adorned with vividly hued oral discs. Photo by Bartek Stańczyk.

The appearance of an individual polyp is greatly influenced by environmental factors. Even polyps of the same species may exhibit disparities not only in the size of their oral discs and polyp length but also in the intensity of their coloring. A polyp thriving in stronger currents and abundant light will likely grow shorter with a smaller oral disc compared to its counterpart in low-light, low-current conditions.

Zoanthus polyps orients themselves toward the source of light. Photo Bartek Stańczyk

Given that the majority of corals within the Zoanthidae family harbor symbiotic Zooxanthellae within their tissues, Zoanthids rely on light for their survival.

How do Zoanthids reproduce?

In their natural habitat, these organisms exhibit the ability for both sexual and asexual reproduction. While there is limited research on sexual reproduction within the Zoanthidae family, aquarists demonstrate greater interest in asexual reproduction. In Zoanthids, this process typically involves budding, where a new polyp emerges not from the tissue of another polyp, but rather from tissue developing on the substrate.

Corals for beginners

Until recent years, Zoanthids were commonly regarded as one of the simplest corals to maintain in a marine aquarium. Alongside other soft corals, they served as the foundational inhabitants of tanks established by the beginners, who, as they delved deeper into the intricacies of the marine realm, eventually transitioned to more challenging and calcifying corals, which demand greater expertise to cultivate.

Several factors contribute to the ease with which Zoanthids can be propagated. Firstly, they exhibit considerable resilience to fluctuations in water parameters, thus accommodating mistakes made by inexperienced aquarists. Secondly, under favorable conditions, they proliferate readily, swiftly enveloping the substrate upon which they reside. Thirdly, they lend themselves readily to fragmentation, facilitating the creation of new cuttings for trading or exchange. Fourthly, they display relative resistance to disease and encounter few natural adversaries. Finally, they require minimal specialized care.

Great comeback

Around a decade or so ago, the selection of Zoanthids in marine aquarium stores was rather limited, to put it mildly. Only a handful of basic color variations were typically available. This scarcity may have stemmed from the practice of hobbyists sharing Zoanthids among themselves, leading to their widespread proliferation to the extent that they were sometimes viewed akin to weeds. In online forums, discussions began emerging regarding fish species capable of managing Zoanthid populations.

Presently, Zoanthids are experiencing a veritable resurgence in the realm of marine aquaristics. This trend has been unfolding for several years now, as remarkably vibrant varieties, often exhibiting fluorescence, have begun to grace the shelves of aquarium shops. Recognizing their market potential, salespersons swiftly capitalized on their appeal, with the rarest color variants fetching prices upwards of several thousand dollars per polyp.

Zoanthids offer hundreds of color varieties, and thanks to the phenomenon of fluorescence, some of them can glow under UV lighting. Photo B. Stańczyk

Thus, Zoanthids have reclaimed their position at the forefront of aquarium enthusiasts’ attention, with tanks adorned by their diverse color variations eliciting awe. This spectacle is all the more captivating given that these corals do not necessitate expansive tanks or elaborate filtration systems, unlike SPS corals. By concentrating a few distinct varieties within a confined area and enhancing illumination with additional UV LEDs, one can savor truly breathtaking vistas.

Coral breeders specializing in “high-end” Zoanthid varieties continue to coin captivating names such as Samurai Sunrise or Ice and Fire. However, these monikers bear no relation to scientific taxonomy, and it’s entirely plausible for the same coral to be marketed under different names by various sellers. Regrettably, it often transpires that rarity is not without cause. Many of these “ultra-colored” varieties exhibit slower growth compared to their more commonplace counterparts. While they remain relatively straightforward to cultivate, they are no longer dismissed as mere weeds.

Water parameters for Zoanthids

As previously mentioned, Zoanthids possess a notably thick and sturdy tissue, affording them some protection against fluctuations in water parameters and mitigating the impact of chemical fluctuations. However, this resilience does not negate the necessity for stable water chemistry. On the contrary, it is precisely within a stable environment that they thrive, showcasing their vibrant colors. Frequent fluctuations in salinity and water composition can induce stress and hinder their ability to reveal their beauty. Their specific requirements align with standard aquarium water parameters, thriving in water with consistent parameters: temperature ideally between 25-27°C, salinity maintained at 33-36 ppt, and pH levels within the range of 8-8.3.

While Zoanthids are not excessively demanding, maintaining stable and optimal water parameters is essential to enhance their colors. Photo by Bartek Stańczyk.

Regarding nutrient levels of NO3 and PO4+, it’s generally understood that Zoanthids do not favor zero levels. This is attributed to two factors. Firstly, these corals predominantly rely on Zooxanthellae for nutrition, and as photosynthetic organisms, these organisms necessitate nitrates and phosphates. Secondly, due to their substantial biomass and relatively rapid growth compared to SPS corals, Zoanthids particularly require phosphates to sustain numerous metabolic processes within their growing tissue. Consequently, Zoanthids, alongside other soft corals such as Sinularia, Sarcophyton, Rhodactis, thrive in water where detectable levels of nitrates (approximately 5-10 mg/l) and phosphates (0.1 g/l) are present.

Where to put Zoanthids in the aquarium?

While Zoanthids rely on light for growth, they should not be positioned directly under intense light sources such as LED panels or HQI lamps. Excessive illumination, particularly if introduced abruptly, as may occur when new varieties are added to a brightly lit aquarium without acclimatization, can induce oxidative stress and, in severe cases, even lead to tissue regression in the coral.

In instances where intensive lighting is employed in the aquarium, perhaps due to the prevalence of SPS corals, Zoanthids are best situated close to the substrate or in partially shaded areas, such as beneath rock overhangs, rather than in complete darkness. It’s imperative to identify an optimal location, as Zoanthids tend to develop smaller oral discs in bright light and may lose their vibrancy in excessively dark conditions. Fortunately, relocating Zoanthids within the aquarium poses no significant challenge, facilitating the search for an ideal placement.

Regarding water circulation, a moderate flow is recommended, ensuring that polyps are not buffeted by strong currents but rather gently swept to dislodge any residual detritus between them. Zoanthids readily adapt to aquarium conditions, provided they remain optimal and consistent.

Zoanthids adapt very easily to the aquarium situation – as long as it is optimal and unchanging.

Are Zoanthids aggressive/expansive?

While most Zoanthids possess cnidocytes, these structures are not notably active or effective in paralyzing potential prey. Laboratory experiments have indicated that some species rarely employ their stinging capabilities, even when directly provoked by artemic larvae. Furthermore, given the short and rigid nature of Zoanthids’ arms, it is evident that these popular corals are not particularly predatory. Although equipped with nematocysts, which could theoretically pose a threat to neighboring corals, instances of Zoanthids stinging each other, especially among different color varieties, are seldom reported.

It’s rare for Zoanthids of different color varieties to sting one another. Photo Bartek Stańczyk

The debate over which coral would emerge victorious in a hypothetical battle would likely be protracted. With limited research on the topic, our understanding primarily stems from anecdotal and often conflicting information provided by aquarists themselves. Nonetheless, it stands to reason that even if Zoanthids were to lose such a skirmish, their capacity for rapid colony growth could pose a threat to other corals. Certain varieties of Zoanthids, under optimal conditions, can proliferate extensively, making it advisable to position them on separate rocks to prevent colonization of other substrates. Conversely, clustering them closely together can accentuate color variations and create a visually striking display.

It’s important to recognize that Zoanthids, like numerous other corals, have the ability to detach several polyps in extreme circumstances, a phenomenon known as polyp bailout, allowing them to drift away and settle in a new location. This response typically occurs in reaction to stressors such as excessively strong water currents. I have personally observed this behavior on numerous occasions, even when there was limited space available for new polyps on the rock.

Feeding Zoanthids

Zoanthids are animals, which means they must obtain their food themselves. Many soft corals have thick tissue that provides ample space for Zooxanthellae. Consequently, these corals heavily rely on photosynthesis for sustenance, reducing their need for heterotrophic feeding. This has perpetuated a misconception in the aquarium hobby that soft corals can thrive without additional feeding. While many can indeed survive in aquariums without extra food, they still absorb organic matter from the water. To enhance the vibrant colors of corals, supplementary feeding is recommended. This helps prevent an excess of Zooxanthellae and promotes optimal coloration.

How to feed Zoanthids?

Zoanthids are ideally fed during the daytime, as many of them retract their polyps at night. An excellent choice for feeding is Tropical Marine Power Food SPS Powder or wetted food Tropical Marine Power Food SPS mini granules. Since Zoanthids do not actively capture sinking food, it’s advisable to temporarily pause the circulation and delicately administer food using a pipette.

Take care not to agitate the polyps excessively, as they will promptly retract if irritated. It’s preferable to gently distribute the food over the polyp colony and allow it to settle naturally onto the corals. After a few minutes, the circulation can be resumed to disperse any remaining food, which will be consumed by other aquarium inhabitants.

Tendency to diseases

Similar to other organisms, Zoanthids can be susceptible to various health issues. Aside from aquarium conditions causing stress, such as fluctuations in salinity or lighting, Zoanthids commonly encounter problems for two main reasons.

Firstly, they may fall victim to organisms parasitizing their polyps, such as snails and spiders. These pests not only irritate the corals but also inflict damage to their tissue, ultimately resulting in the gradual demise of the colony. The most effective method for dealing with these unwanted guests is to subject the affected corals to a disinfectant bath. Additionally, it’s advisable to inspect the polyp roots, as parasite eggs are often found there.

The second prevalent issue is bacterial infection, known as Zoa Pox. Symptoms include closed polyps exhibiting signs of tissue regression, along with the presence of white “pimples” and discoloration. The most effective treatment for bacterial infections typically involves subjecting affected corals to baths of new cuttings in a 3% hydrogen peroxide solution or in an antibiotic solution. Nitrofurazone and chloramphenicol are particularly potent antibiotics in combating such infections.

Do Zoanthids contain palytoxin?

Palytoxin stands out as one of the most potent non-protein toxins, and indeed, certain corals contain significant amounts of it. These corals fall into three groups: Palythoa, Protopalythoa, and a select few species of the genus Zoanthus.

A scientific study published in the Toxicon Journal in 2009, though potentially outdated, lists several species of Zoantharia containing palytoxin, including Palythoa caribeaorum, P. mammilosa, P. tuberculosa, P. toxica, P. vestitus, P. aff. margaritae, Zoanthus soanderi, and Z. sociatus. However, it’s worth noting that this publication dates back to 2009 and may not reflect current knowledge.

Thankfully, the majority of colorful Zoanthids belong to the Zoanthus vitenamensis varieties, which do not contain this toxin. Nevertheless, as there is no readily available and inexpensive test for the presence of palytoxin, it’s important to exercise caution when handling Zoanthids, especially outside of water. Safety glasses and gloves should be worn, and all fragging should be conducted in a well-ventilated environment.

I hope I’ve been able to showcase the beauty of Zoanthids. Their vibrant colors rival those of other corals and often surpass them in intensity and diversity. I encourage all marine aquarium enthusiasts to consider adding them to their tanks, particularly in mixed reefs. However, the most striking tanks are those adorned solely with Zoanthids, enveloping the rockwork and substrate. With dedication and care, the results can be truly astonishing.

Bartek Stańczyk

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