VIVO_2-2013-en

VIVO Corals 09 by Johannes Dürbaum Stony corals are very popular, among others due to their coloration. Whenever “new colors” of a species appear in the trade, these are very much sought after and therefore may cost several times as much as the already known color morph. This is a reason for vegetative multiplication by means of fragments (“fragging”). W here does the color of stony corals come from? Colors originate from different ab- sorption and reflection of light. Upon close observation, not only the coral animals themselves – the so-called polyps – have such pigments within their tissue, but also the single celled endosymbiotic zooxanthellae with their ambivalent animal and plant character that live within the coral tissue. Zooxan- thellae mainly belong to the dinoflagellates, which neither belong into the plant nor the animal catego- ry. They have flagellae on the outside for moving, thus they have animal characteristics. However, they have chloroplasts inside where chlorophyll and other pigments productive in metabolism can be found, just as in a photosynthetically active plant cell. Light intensity is crucial for the productivity of the zooxanthellae and, subsequently, for the growth of the coral. As in photosynthetically active plants, there is an optimum in photo synthesis performance. If the irradiation is increased beyond this optimum, the production of glucose breaks down as photo syn- thesis processes are being inhibited. The complicat- ed energy transfer and bond chain breaks down be- cause of overload – from the viewpoint of the animals, this is exactly what must be avoided. Coral colonies of the same species often live in different depths and, correspondingly, in entirely different lighting scenarios. Apparently, certain species have found ways to live lastingly with such different living conditions, in spite of their intense light require- ments. Pigment distribution is involved here. Being energy fixating organisms, the zooxan- thellae are not distributed randomly within the coral tissue. When particularly much light – as at the ocean surface – is present, they retreat deeper into the cor- al tissue, the pigment layer lies on top and serves as a filter. Light hitting the pigments is reflected as col- ored light. Consequently, only a part of the irradia- tion hits the zooxanthellae. This protects them against excess light and inhibition. However, the zooxanthellae are located in the upper tissue layers in the deep water forms. The zoo xanthellae literally are thirsting for the little light. The light they cannot trap hits the pigments located deeper, which reflect it to the back side of the zoo- xanthellae. This construction is similar to a light trap. However, corals of the same species can be seen directly adjacent to each other in nature. Colo- nies of Seriatopora hystrix (Pocilloporidae) or Monti- pora digitata (Acroporidae) are examples. Brown and colorful varieties grow side by side. This again sug- gests these are genetically caused preconditions which, however, do not have significant advantages for the symbiosis, otherwise one color morph would at least dominate considerably. So you will require ideal light intensity if you want particularly colorful corals, as to make the pig- ments within the tissues move to the surface. But you will also require the correct light! The numerous zoo- xanthella pigments involved in photo synthesis re- quire certain light wavelengths. This may possibly include low amounts of UV-A and UV-B light, to which the animals, after all, are also exposed in na- ture. The fluorescent pigments in the tissues take up the UV-A and UV-B radiation and “slow it down” to lower frequencies that make them useable for photo synthesis by the zooxanthellae. There is no doubt that certain minerals en- hance the overall color impression of stony coral col- onies and their pigments without being able to trace them in pigments due to the very low concentra- tions. The colors will intensify within a few weeks if you offer these trace elements in the aquarium. How- ever, the nitrate and phosphate water parameters must be close to zero as in nature for achieving this. Deep water: little light Pigments behind the chloroplasts reflect light to the chloroplasts. Shallow water: plenty of light Pigments reflect and protect chloroplasts against too strong light. LIGHT LIGHT Chloroplast Pigment sera marin COMPONENT 3 and 4 contain the trace elements im- portant for natural growth and color enhancement.

VIVO_2-2013-en

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