Zoanthids and Palythoa: A Fan Favorite In The Reefing Hobby - With Special Considerations
Zoanthids and Palythoa: A Fan Favorite In The Reefing Hobby - With Special Considerations!
Zoanthids are often the first coral a new reefer purchases, and for good reason. They are hardy, colorful, fast-growing, and tolerant of a wide range of conditions. However, labeling them as simply a beginner coral overlooks their long-term complexity. At scale, zoanthids become a collection-driven niche with lineage tracking, morph stability considerations, and ongoing management that challenges even experienced reefers.
What Are Zoanthids?
Zoanthids, within the order Zoantharia, are colonial cnidarians composed of individual polyps connected by a shared tissue base. Each polyp contains symbiotic zooxanthellae that provide energy through photosynthesis. The polyp structure includes a central oral disc surrounded by tentacles used for both feeding and environmental response.
Unlike stony corals, zoanthids do not build a rigid calcium carbonate skeleton. Instead, they grow by encrusting over rock or substrate using soft tissue.
Palythoa are closely related and frequently confused with zoanthids. In general, Palythoa tend to have larger polyps and form thicker, more continuous mats. They often incorporate sand and debris into their tissue, giving them a more rigid and textured appearance. Zoanthus species typically have more distinct individual polyps with less incorporation of substrate material. Identification in the hobby is inconsistent, and many specimens are mislabeled.
Environmental Tolerance Versus Optimal Conditions
Zoanthids are tolerant of a wide range of conditions, but tolerance should not be mistaken for optimal health. They will survive in elevated nutrient systems, but coloration, growth structure, and long-term stability improve significantly under balanced conditions.
Nitrate is best maintained between approximately 2 and 15 ppm. While zoanthids can tolerate higher levels, coloration often becomes muted above 20 ppm. Phosphate is ideally maintained between 0.03 and 0.15 ppm. Elevated phosphate can increase algae competition and inhibit clean growth edges.
Stable alkalinity between 7.5 and 9 dKH is recommended, with stability being more important than a specific number. Salinity should remain consistent at 1.025 to 1.026, and temperature should be held between 76 and 80 degrees Fahrenheit with minimal daily fluctuation. pH in the range of 8.0 to 8.3 supports normal metabolic function.
Lighting
Zoanthids adapt to a wide range of light intensity, but their coloration and morphology are strongly influenced by spectrum and stability.
Most zoanthids perform well between 100 and 200 PAR, typically placed in the mid to lower regions of the aquarium. Lower light morphs can tolerate around 50 PAR, while some higher light tolerant morphs can adapt to levels approaching 250 PAR if properly acclimated.
Blue-heavy spectrum lighting enhances fluorescence and color contrast. Excessive white intensity often results in washed-out coloration and can increase nuisance algae growth on the colony surface.
Signs of excessive light include bleaching and retracted polyps (Fig 1. Insufficient light often results in stretching (Fig 2), where polyps extend upward in search of higher intensity.
(Fig 1.) Bleached & Retracted
(Fig 2.) Stretched zoanthids looking for light
Flow
Flow is a critical but often underestimated factor in zoanthid health. They require low to moderate, indirect, and turbulent flow.
Proper flow keeps detritus from settling between polyps and reduces the risk of bacterial irritation. Direct, high-velocity flow will cause polyps to remain closed. Conversely, insufficient flow allows debris accumulation, which can lead to localized tissue irritation and increased pest susceptibility.
Feeding
Zoanthids rely primarily on photosynthesis but will benefit from supplemental feeding, especially in systems with controlled nutrient levels.
Fine particulate foods and broadcast feeding methods are most effective. Target feeding is generally unnecessary for most colonies.
Supplemental feeding can increase growth rate and polyp size. However, excessive feeding can elevate nutrient levels and contribute to nuisance algae growth, which can negatively impact colony health.
Growth Behavior and Competition
Zoanthids exhibit both physical overgrowth and chemical interaction with neighboring corals.
Fast-growing morphs can quickly encrust over slower-growing varieties, leading to loss of diversity in mixed colonies. Some zoanthids also release compounds that inhibit nearby corals, particularly in densely packed systems.
Spacing and intentional placement are important. Isolating aggressive growers on separate rocks or designated sections helps maintain long-term structure and prevents unwanted dominance.
Building a Zoa Garden
A successful zoa garden requires planning rather than random placement.
Flat rock structures or ceramic surfaces provide the best visual presentation and allow each morph to be viewed clearly. Placement in moderate flow and stable lighting zones promotes consistent growth.
Grouping morphs by similar growth rates and light preferences improves long-term success. Faster-growing varieties should be given space or isolated to prevent them from overtaking more delicate or slower-growing morphs.
Periodic fragging is necessary to maintain boundaries and prevent overgrowth. A zoa garden is not static and requires ongoing management to preserve structure and diversity.
Common Pests and Irritants
Zoanthids are susceptible to a range of pests that can quickly impact colony health.
Zoa-eating nudibranchs are one of the most common and destructive pests. Sundial snails and small spider-like predators called Zoa Sea Spiders (sea spiders or Pycnogonids) are also frequently encountered. Hydroids and nuisance algae can irritate tissue and inhibit polyp extension.
All new frags should be dipped using a coral-safe dip solution. Visual inspection of the plug, underside, and colony edges is critical. Repeated dips may be necessary if pests are detected, as a single treatment is often insufficient.
Fragging Zoanthids
Fragging zoanthids is straightforward when done properly.
A sharp scalpel or coral cutters should be used to separate polyps at the base of the mat rather than cutting through the polyp itself. Frags can be mounted using gel super glue onto clean plugs or rock.
After mounting, moderate flow helps prevent detachment. Most frags will reopen within one to three days and resume normal growth within one to two weeks.
Palytoxin Safety
Palythoa species can contain palytoxin, a highly potent biological toxin. While incidents are rare, exposure can be serious.
Risk increases when colonies are cut, crushed, or exposed to conditions that aerosolize tissue. Activities such as scrubbing live rock with palythoa or using tools that generate fine particles should be avoided.
Gloves and eye protection should always be used when handling these corals. Direct contact with eyes, mouth, or open wounds should be avoided, and hands should be washed thoroughly after handling.
Long-Term Considerations
Zoanthids are easy to keep initially but require increasing management as colonies grow.
Long-term success involves controlling growth, preventing pest outbreaks, maintaining coloration across lighting zones, and preserving morph separation. Systems that begin as simple frag collections often evolve into carefully managed displays that require regular intervention.
Conclusion
Zoanthids are often considered a beginner coral, but they remain relevant at every level of reef keeping. They provide a practical foundation for understanding nutrient balance, lighting control, flow dynamics, and coral growth behavior.
With proper management, they can develop into complex, curated displays that reflect both skill and long-term system stability.
SAFETY WARNING: It is also important to recognize that while zoanthids are generally safe to handle, closely related Palythoa species can contain palytoxin, a highly potent biological toxin. Proper handling practices, including the use of gloves and eye protection, should always be followed when working with these corals, especially during fragging or removal.
Disclaimer
This content is intended for educational purposes only. Information may change as reefing practices evolve and new data becomes available. First Due Aquatic Rescue is not responsible for outcomes resulting from the use of this information. Always verify guidance across multiple reputable sources.