Zoanthid Coral Care Guide

Zoanthid polyps close or fail to open due to pests, flow issues, lighting stress, or counterintuitively, nutrient levels that are too low. Zoanthid-eating nudibranchs are the most common culprit—these tiny predators camouflage themselves by mimicking the color of the colonies they eat, making them nearly invisible until inspected closely with a flashlight. Sea spiders (pycnogonids) and Sundial snails also devastate colonies but hide within closed polyps. Wrasses including Six Line, Leopard, and Melanurus effectively control nudibranch populations.

Flow problems occur when direct powerhead output forces polyps closed or when insufficient flow allows debris to accumulate on the mat. Many reefers discover that zero nitrates actually prevents polyp opening—Zoanthids need some nutrients (5-15 ppm nitrates) and will stay closed in ultra-low nutrient systems. Newly introduced colonies can remain closed for 2-7 days during normal acclimation.

Zoanthid growth rate varies significantly by species, lighting, feeding, and water quality. Some larger colonies can add 5-20 new polyps per month under the right conditions. Well-fed colonies in stable reef systems with moderate lighting and nutrient availability spread rapidly across adjacent rockwork, with the encrusting mat extending outward as new polyps form. Some aggressive-spreading varieties can double in size within 3-6 months, while slower-growing species or colonies in suboptimal conditions may add only one or two polyps per month.

Zoanthids spread faster when target-fed small meaty foods like frozen mysis shrimp or zooplankton, and when provided with stable parameters including alkalinity around 8-9 dKH and nitrates in the 5-15 ppm range. Reef keepers concerned about overgrowth can control spread by regular fragging or creating physical barriers between colonies and other corals.

Zoanthid corals are photosynthetic and receive most of their nutritional needs from zooxanthellae algae living in their tissues, but target feeding accelerates growth and color intensity. Reef keepers can feed colonies small meaty foods including frozen mysis shrimp, frozen cyclops, reef roids, or specialized coral foods 1-2 times per week by spot-feeding individual polyps or broadcasting food when polyps are open. Well-fed colonies display brighter coloration, faster spreading, and better resilience to stress compared to unfed colonies relying solely on photosynthesis.

Target feeding is particularly beneficial for Zoanthids in low-nutrient systems or under lower lighting where photosynthesis alone may not provide optimal nutrition. Overfeeding should be avoided as excess nutrients can lead to algae growth on the mat, which can inhibit polyp opening and health.

Zoanthid propagation involves cutting or peeling a section of the colony mat with several polyps attached and securing it to new rockwork or frag plugs using gel superglue or rubber bands. Reef keepers should wear protective gloves and eyewear due to palytoxin risk, use a sharp razor blade or scissors to make clean cuts along the mat between polyps, and minimize time out of water to reduce stress. The fragged section can be glued directly to dry frag plugs or rock using gel superglue, which cures quickly underwater and forms a strong bond.

Expect newly fragged colonies to be closed for at least 1-3 days, though most usually open and show signs of healing quickly if water conditions are good.

Zoanthid placement depends on the specific variety and lighting, with most species thriving in the bottom third to middle of the reef tank where PAR levels range from 80-120. Lower-light varieties like browns and greens perform well in shadier spots receiving 50-80 PAR, while high-light designer morphs often need 100-150 PAR in mid-tank areas for their best coloration. Colonies should be placed where they receive gentle to moderate flow that creates slight polyp movement without bending them over, typically away from direct powerhead blast.

Allow plenty of room to spread since healthy colonies expand rapidly across adjacent rock—avoid placing them next to slow-growing or delicate corals that could get overgrown. Start new colonies in lower light and gradually move them to their permanent spot over 1-2 weeks to prevent bleaching from light shock.