Zoanthids are marine coral of the phylum cnidarian. Popular with aquarists, these soft coral formations provide marine aquarium hobbyists with a broad range of decorative color, shape and size options.
Tropical oceanic reef habitats offer brilliant displays of life; zoanthid corals play a vital role. Marine aquarium enthusiasts rate zoanthid corals as hardy and often recommend them to beginners for their ease of care. Purchased in fragments, zoanthids are aquatic invertebrates of individual polyps who colonize. These gelatinous groupings of soft coral attach onto a piece of live rock, or other hard reef structure, where they feed, grow and propagate.
Healthy zoanthids need specific water conditions and weekly testing for alkalinity, iodine, calcium, magnesium, temperature, nitrates, phosphates and pH should be conducted. While zoas can survive in less than perfect water quality conditions, they will not thrive, grow or produce desirable colorful displays. Water chemistry is important, so a good test kit will be a lifesaver. Readouts from standard marine water test kits are delivered in numbers indicating parts per million. Alkalinity, or dKh, can be delivered via a kalkwasser drip, and needs to be between 8.0 to 9.0 on the test kit. Calcium, also delivered with kalk drip, should be between 420 to 440. A healthy level for magnesium is 1,250 to 1,350. Water temperature should be 79 to 80 degrees, pH 8.1 to 8.2, phosphates .02 to .03 and nitrates less than 5. Marine aquarium water parameters are regulated with regular water changes.
Lights and Action
Zoanthids need the proper lighting to survive. Metal halide lights with actinic supplementation work best. The actinic light supplies the ultraviolet and X-rays required for photochemical effect, giving zoas their glowing appearance. Zoanthids have different lighting requirements and aquarists usually group zoas who prefer light, and apportion one side of their tank for zoas who prefer shade. Zoas are available in brown/gray, bright orange, red, green, yellow and blue and a variety of color morphs. The coloration seen with Zoas is not simply the handiwork of their own pigments, but derived from a symbiotic relationship with an algae, zooxanthellae, which adhere to their surface tissue.
Feeding, Currents and Potential Predators
Feeding zoanthids is breed specific, but target feeding is a favored practice. Target feeding involves shutting down the water flow and placing fare directly onto the exposed polyps. Aquarists are often tempted to overfeed zoas in an attempt to accelerate the growth process. While this works, it also causes filtration problems. Most zoas prefer moderate water currents and will adapt to a varying water flow, but anything other than moderate will impact their growth potential. For example, in a high-flow tank, zoanthid polyps will grow closer to the base and develop shorter stalks. The biggest living threat to zoas is the sundial snail. This underwater home wrecker feeds on zoa colonies, causing fading and eventually death. Another consideration for zoanthids is habitat compatibility. Before incorporating any marine life to your tank, be certain it does not feed on coral. Angelfish, triggers, rabbit fish and some nudibranchs are potential predators; an algae bloom can smother zoanthids.