Corals need several types of food. Corals have a mouth and an organ for digestion/stomach (gastrovascular cavity). “Food” is such a broad range of things when it comes to corals. Because “food” to a coral means both proper lighting and plankton….
The most important type of cells that reside within a coral is the Epitheliomuscular cells. These are a specialized type of cell in the epidermis that have muscle fibers for movement and contraction of the polyp. Without these cells corals would not be able to capture food, open and close due to variations in light, or protect themselves again harmful predators. As most people can guess that means that these little muscle fibers need a great deal of energy.
In the majority of corals, the gastrodermis is also home to Zooxanthellae. Zooxanthellae is a type of unicellular algae. Zooxanthellae are responsible for the coloration of the coral. If the zooxanthellae die, the coral undergoes a nasty transformation known as coral bleaching. This is essentially exactly as it sounds. The coral loses its’ coloration and turns white. The Zooxanthellae resides within the corals’ tissue in what is called a symbiotic relationship. This is where two organisms reside together in the same area and usually at least one benefits from the relationship they have. Zooxanthellae are photosynthetic organisms. They harness light and transform the light into energy-rich compounds, which are then transferred to the coral polyp.
One rather important factor about zooxanthellae is they need certain nutrients, such as nitrogen and phosphate, to survive and continue photosynthesis. Zooxanthellae can acquire these nutrients from the coral polyp. BUT, the coral polyp can only obtain these nutrients that are so essential to the Zooxanthellae through the capturing and digestions of plankton and other food it eats. One cannot survive without the other, Zooxanthelae and coral polyp, and in the long term both will perish without the other performing the tasks that it needs to.
This leads us to our next part about light. There's are so many rumors about light and what each reef organism needs. Just because a coral can survive under a certain lights doesn't mean it should. We've had numerous pictures sent to us from people claiming to keep SPS corals under T5s, and then we spot an LED in the reflective water surface. SPS (Small Polyp Stony) corals need at very least STRONG LED lighting with the UV spectrum. Halides are right up there with LEDs. LPS (Large Polyp Stony) corals we only recommend be kept under quality LED lights that are slightly on the stronger side. T5s can be acceptable to soft corals, as even here we have had decent luck with them. We will always recommend however that LEDs or Halides are used to keep any sort of coral or light intensive invertebrate.
When it comes to coral placement it is exactly the same as the light intensity that the specific coral type needs. SPS corals should only be kept closest to the lights, or higher up in the tank. LPS corals should only kept mid-way up the tank and at very least off of the floor of the tank. Soft corals should really only be kept on the bottom of the tank and maybe an inch or two up from there. Keeping light intensive corals any lower can potentially result in "bleaching"; which means that coral loses its color and turns white. Keeping LPS and Soft corals any higher can result in the "burning" to the point they basically lose all pigmentation and simply perish. These are just basic guidelines as all tanks and lighting are different.
If there are any other questions about corals, feeding, placement, lighting, or otherwise, please contact us.