Pulsing Xenia

Care

Xenia species comprisea large group of attractive stalked soft corals with small, non-retractile pinnatepolyps that can contract and open in a rhythmic manner, hence the "pulsing" common name. Most of the 60+ species have a short, smooth, thick unbranched stalk, although branching occasionally occurs in some specimens. The stalks are usually translucent or white with small brown, cream, or greenish coloured, eight-tentacledpolyps - the degree of "feathering" of the individual polyps being highly variable. The polyps of Xenia differ from those of the similar-looking Antheliacorals in that Xenia polyps always arise from a definite capitulum at the terminal end of a stalked base, whereas those of Anthelia always arise directly from the basal encrusting mat. Xeniagenerally form smallish-sized colonies, many rarely taller than a few inches; they are among the first corals to colonise a reef, as they are able to "walk" to new sites by systematic attachment and detachment of their stalks to adjacent locations. In this manner, they can quickly colonise new areas, in some cases even overgrowing other living corals and algae. Interestingly, even within the same species, there may be vast variations in characteristics depending on environmental conditions, such as the size of the stalks, anthocodiae, tentacles, and pinnules. Colonies in deeper waters have evolved with elongate anthocodiae and thinner tentacles, whilst those from strongly lit shallower areas have shorter,more robust polyps. The distinctive recurrent pulsing actions of the polyps can be absolutely mesmerising, however, this behaviour is not yet fully understood(current thinking is that it is related to respiration and gas exchange, rather than nutrient uptake). Not every single specimen can be counted upon to pulse -this is thought to be promoted or discouraged by a whole host of different stimuli, and it is not necessarily an indicator of declining health if the animal is not pulsing. In addition to this pulsating behaviour, these corals are also capable of bending or twisting single tentacles. The home aquarium should be mature and offer plenty of room for the Xenia to spread, which it is likely to do at a fairly fast rate once settled. Aquacultured specimens tend to be much hardier than their wild-collected counterparts, so are the best choice when purchasing for the greatest chances of long-term success. Provide strong lighting and good water circulation around the colony, without vigorous current being aimed directly at the polyps. These corals do not tend to cope well with rapid changes in pH and appear very sensitive to a high pH, so much care should be taken if adding kalkwasser to the aquarium to prevent the pH from rising too quickly. Experts remain very divided when it comes to the use of iodine supplements in aquaria containing Xenia corals; many believe this is a necessary addition for continued good health, yet others have reported no benefits whatsoever (some even reporting adverse effects). Xenia are considered one of the least toxic group of corals, lacking the potent nematocysts of some of the more aggressive genera. However, be aware that a few Xenia species do produce defensive chemical substances called terpenoids in order to deter predators, and this can cause significant damage to some stony corals. Normally with appropriate filtration any toxins that are released can be efficiently dealt with and should not affect your reef. However, it is important to remember that as your Xenia colony grows larger, these toxins may begin to build up if infiltration is not stepped up accordingly and this may start to affect the health of your reef. This is not meant to put you off of purchasing one of these fascinating corals (and indeed it does not even apply to every single species of Xenia) but it is something to be aware of as your colony matures, just in case. It is not uncommon for Xenia to colonise the vertical substrates in the aquarium, including the glass, and this can create a very nice background display. In the wild, many colonies grow on vertical surfaces, and this helps them evade predation by polychaete worms living in the substrate. Other predators to avoid or watch out for include horned seastars (Protoreasterspp.), a handful of small crab species that may come in on live rock (so observe carefully!), and also an amazingly camouflaged nudibranch that cleverly mimics Xenia polyps.

Feeding

Although this is azooxanthellate species, which also utilises dissolved nutrients in the aquarium, it does require supplemental feeding for best long-term health e.g. zooplankton and other foods designed for filter-feeding invertebrates.

Propagation

Xenia spp. are hermaphroditic and reach sexual maturity between 1 and 2 years of age. They employ several different methods of reproduction and are very easy to propagate. When settled, Xenia spp. reproduce rapidly by fission or division (lifting and attaching the stalk to a nearby adjacent surface and then splitting the stalk in two), and careful observation may be required to ensure it does not crowd out or overgrow other species. If propagating from cuttings, ensure that the piece of Xenia in question is removed from the main aquarium before cutting longitudinally between the branches with a sharp scalpel. This is because when handled too roughly, or when cut or injured, Xeniasecrete chemicals into the water that can cause problems for other inhabitants. Cuttings can be attached to small pieces of rock using a loosely tied rubber band or similar, and after a short time, the stalk will adhere to the new substrate (do not tie on too tightly as the coral tissue of Xenia is particularly soft and easily damaged). Colonies that are growing on flat surfaces such as the aquarium glass can be gently eased off with a razor blade and attached to a piece of rock as mentioned above. However, by far the easiest no-fuss method is to place small pieces of rubble adjacent to the growth direction of the colony and let nature take its course. Once colonised, the small pieces of rubble can then be moved where desired. Certain specimens also drop pinnules from the polyps and these attach to the substrate to begin new colonies. In some captive environments, a few species will expel free-swimming larvae called planulae, after brooding them in pouches among the polyps and below the anthocodiae.