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Xenia (Lamarck 1816) species are hallmark "Pulse corals" that are usually stalked, and sometimes branching, with polyps restricted to the cap/crown (capitulum). Xenia polyps may be long, will often pulse, but are never retractile; their polyps will contract (shrink), but never actually retract into the cap/crown. The morphology and color of Xenia species (and those still unproven specimens that we call by a given species name) is variable, but popular "types" include: Xenia elongata (the common, brown "Fast-pulse" Xenia), Xenia umbellata (white "Pom-pom" Xenia), and an iridescent blue-green species that strongly resembles X. elongata (AKA "Silver-tip Xenia"). Hobbyists hold many more varieties in collections, from nappy, yellow, Red Sea clusters to red-hued Indonesian colonies, and numerous other members of the genus found in colors ranging from cream to green and through to dark brown. With perhaps more than 60 species in this genus, Xenia are widely distributed from the east coast of Africa through to the central Pacific. They are generally found in clear, bright, shallow waters with moderate to strong water flow. Although most Xenia are not common from turbid or dirty waters, they will colonize early upon stressed or damaged reef areas resulting from pollution and natural disaster. A closer look at their physiology reveals that Xenia have weakly developed structures for organismal feeding; nutrient uptake of dissolved matter is conducted in this heavily photosynthetic genus. Target feeding of Xeniids is not required (if it's even practical or possible) to cultivate them successfully in aquaria when there is an adequate supply of nutrients available otherwise (bio-load of fishes and other invertebrates, etc.).

Once acclimatized, most Xeniids are fast growing and may even be considered invasive under certain circumstances. It stands to reason that such successful species are readily consumed by dedicated corallivores and casual browsers of cnidarian tissue. Typically "reef-safe" fishes like tangs will often nibble Xeniids… and dubious characters like angelfishes will often make a beeline straight for a new colony placed in the tank! It's a good idea to establish Xeniids separately, as in refugia, up to several weeks in advance for their safety before introducing them to the main display. Since they do not feed significantly on large solid matter/plankters, they are quite safe to keep in a (coral) food-producing refugium with little burden to the functional benefits of the vessel. In fact, Xeniids are sometimes used as "animal filters" much like macroalgae with "vegetable filters" for nutrient export because of their fast growth, salability at harvest, and for their negligible imposition on most other desirable life forms in refugia.

Anthony Calfo

For a more detailed discussion of Xenia, see Anthony's feature article in the February 2004 issue of which this text is excerpted.

Special thanks to Jonathan Bertoni (bertoni) for his assistance on this project.