Natural seawater has about 60 parts per billion of iodine, including all forms such as iodide, iodate, and organically bound iodine. This value is the standard for natural oceanic seawater, away from coastal influences. We suspect that iodine values in coastal water are somewhat higher, as a result of concentration of iodine by algae in their tissues, and subsequent release of organic iodine when the algae decompose. If this is true, then oceanic reefs may be more iodine limited than coastal reefs.
Iodine (as iodide) may be added in the aquarium in several different forms. The most commonly used form is potassium iodide. The stock is prepared by adding 25 grams of potassium iodide to 0.5 L of pure water. This is added to the aquarium at a rate of 0.5 mL per 100 L per two weeks (Wilkens, 1973). Other options for sources of iodine include Lugol's solution, organic sources of iodine, and tincture of iodine. Organic sources of iodine, as found in some supplements, afford continuous release of iodide without risk of overdose. Lugol's and tincture of iodine are solutions in which pure iodine lias been dissolved in a solvent of potassium iodide solution. Tincture of iodine contains some alcohol in addition, but this is not a concern or disadvantage considering the small dosages. Lugol's solution, also known as "strong iodine" solution, was brought to our attention by John Burleson and Merrill Cohen. They both found that it stimulated growth in Xenia species, and helped prevent common "crashes" of this soft coral. Interestingly, they both observed that potassium
iodide alone did not have the same effect. It is likely that the benefit of the mixed iodide/iodine solution over just iodide lies in its germicidal property (i.e. its ability to kill bacteria or protozoans that kill Xenia) rather than any nutritive value. However, iodine rapidly converts to iodide in seawater, and therefore it is possible that the benefit is due to greater dosage.
While the dosage for potassium iodide is known, as described at the beginning of this discussion, the limits for Lugol's and tincture of iodine are less clear. We have safely administered one drop from an eyedropper per 80 L (20 gal.) aquarium capacity weekly. Take one drop at a time diluted with some aquarium water in the eyedropper, and either administer it over the target organism, be it a Xenia sp., or Dictyota or Sargassum algae, or simply add it in the stream of current from your pump return. Lugol's solution is not a common item on the shelf at your local drugstore, but most pharmacies are able to order it for you, if you are patient enough to wait. Tincture of iodine is available at. grocery stores and pharmacies everywhere. There are numerous aquarium industry companies now marketing iodine supplements, and these can be bought from your pet dealer. It is safest for the hobbyist to buy these and follow the directions.
Iodine (as iodide) appears to be essential for the long term maintenance of Xenia and certain algae, it is beneficial to other soft corals, especially Anthelia spp. and Clove polyp (Clavularia sp.). Iodine additions are also absolutely critical for long-term success with stony corals. Unfortunately, there are few scientific papers which describe the importance of iodine to coral health, so our comments will appear anecdotal to scientists. Iodine is an integral part of skeletal proteins in gorgonians (see Ciereszko and Ivarns, 1973), and it may be that it plays a similar role in other hermatypic organisms.
Furthermore, iodine may detoxify active oxygen produced by photosynthesis (R. Buddemeier, pers. comm.). This may partially explain the observed benefits to corals and anemones, particularly with respect to bleaching, as we shall describe. See the topic of toxic oxygen in chapter 6 and bleaching, chapter 10.
Based on observations in our own aquaria, confirmed by our communications with A. Nilsen and D. Stüber, and prior work by Peter Wilkens, it appears that iodide is critical for the development of pigments in corals, corallimorpharia, and anemones, both the golden brown of the zooxanthellae and the green and red colours
of accessory7 pigments. Alf Nilsen observed a link between coral bleaching and subsequent poor health with iodide deficiency. Corals that appear to be suffering from light shock can be cured, that is, their ability to adapt to the light can be restored, with iodide additions. What this indicates is that in an iodide deficient system, corals and anemones cannot easily adapt to changes in light.
Corallimorpharian "Mushroom anemones" expand and become most colourful when iodine and other trace elements are routinely replenished. J.C. Delbeek.
We have also seen greater expansion of mushroom anemones after a routine of iodine additions has been established, and we have noticed that iodine is useful for treating infections which occasionally affect zoanthid anemones. It may be administered directly over the colonial anemones (pers. obs.) and over Xenia (J. Burleson, pers. comm.), but not all invertebrates tolerate direct exposure. Stony corals do not appreciate direct administration of iodine, and will display their displeasure by shriveling up and exuding mucus and mesenterial filaments. Too much added to the tank at once may injure the fish and invertebrates, (pers. obs., and M. Paletta, pers. comm.), and can stimulate the growth of both desirable and undesirable algae (A. Nilsen, pers. comm.). Please see Synergistic effect of Phosphate and Trace Elements in chapter 9 for additional information on algae stimulation. So, a word of caution is in order regarding the dosage. Iodine must not be over-dosed.
The use of activated carbon media, though beneficial in our opinion, may significantly remove iodine from the water. This is not a problem since the plants and invertebrates also remove iodine, and the iodine is easily replenished with supplemental additions. Some other trace elements are also added to reef aquariums with beneficial results. These include iron, molybdenum, barium, and lithium. The exact functions of which in corals are not
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