Corals and Anemones
By far the most well-known reef invertebrates are corals and anemones. They are members of the Cnidaria phylum, which also contains jellyfish and hydroids. All cnidarians contain stinging cells, albeit some are more effective than others. Corals and anemones are members of the anthozoa class. This category has a diverse variety of organisms, but the primary species of interest in reef aquariums are: octocorals (soft corals, gorgonians, and organ-pipe corals), anemones, corallimorphs and zoanthids, and genuine hard corals (also known as stony or reef building corals). Most (but not all) need moderate to acceptable illumination, which power compact fluorescents or numerous standard fluorescents may supply. A few varieties need very bright lighting.
Octocorals contain eight tentacles per polyp and are mostly colonial animals that reproduce mostly by budding. Octocoral stinging cells do not hurt other reef dwellers. All seem glued to rock and are immobile. Some have skeletons composed of loose calcium spines or tubes, giving them the appearance of being hard or stiff, but they lack the solid calcium skeleton seen in real hard corals.
Soft corals are the most widely preserved creatures besides octocorals. Soft corals include leather corals (such as Sarcophyton) and finger leather corals (such as Sinularia). Soft corals like moderate water movement and do not require harsh illumination. They may be maintained with a broad variety of fish and can withstand more nitrate than real hard corals. They like being fed. Gorogonians, sometimes known as sea fans, are occasionally maintained. This is a diverse group that may be demanding. Many species do not need light, although they may be difficult to feed in aquaria and require very high water quality and flow. Organ-pipe corals need relatively little light but are picky about water quality and must be fed. They are occasionally maintained for their colourful bones.
Anemones are most known for hosting clownfish, who are resistant to their stinging cells and shield themselves with the flowing tentacles. Some damsels can do this as well. However, clownfish in aquaria do not spend as much time in anemones as they do in the wild since their need for predator protection is (or should be) nonexistent. Some will not even attempt to utilise an anemone that is accessible, and all will live and grow without anemones. When a clown does utilise an anemone, it makes for an intriguing sight, and anemones are gorgeous in their own right.
Anemones have a delicate body and the ability to move. Some have little tentacles, while others have extremely lengthy tentacles. The tentacles round the body cavity. Anemones reproduce through budding, which means physically tearing themselves apart to make two smaller individuals, or “spawning” a number of miniature copies of themselves. Most aquarium fish are solitary rather than colony. Others anemones rely on photosynthetic algae, which need relatively high light intensities to flourish, while some may do well without high light intensity if fed enough.
Carpet anemones are vividly coloured and low-maintenance anemones. They have small tentacles, are seldom utilised by clownfish, and may deliver a painful sting. The magnifica anemone is the most demanding anemone available. Beautifully coloured and a favourite of many anemones in the natural, they need a lot of light and absolutely perfect water quality. Radianthus anemones, yellow-stem anemones, and bubble anemones are also available. These will not survive high levels of nitrate but will withstand moderate light intensity with frequent feeding.
Corallimorphs and zoanthids
These are often classified as soft corals alongside leather corals, and although they belong to separate orders, their needs are similar. Corallimorphs and zoanthids are connected to real hard corals and anemones more than octocorals. They are often flattened and devoid of bones. Some are fixed, while others may move, but they are typically less mobile than anemones. Corallimorphs and zoanthids are generally tolerant of low water quality and do not need vigorous water movement, although some, especially the extremely brightly coloured varieties, do require adequate illumination.
True hard corals
True hard corals are also known as stony or reef-building corals. In the wild, these corals build down a calcium carbonate skeleton into which they may virtually or completely withdraw their tentacles, contributing to the general development of the reef. With a few exceptions, stony corals get their energy from symbitoic algae inside their tentacles; nevertheless, most also augment their diet. Everyone like chaotic water flow. While not a scientific classification, stony corals may be divided into two major groups: small-polyp and large-polyp.
Small-polyp stony (or SPS) corals depend much more significantly on the algae they contain for life. These are the corals that need a very high light intensity – power compact fluorescents can sufficient in certain cases, but metal halide lighting is sometimes required in deep tanks. SPS corals are also the most picky about water quality, and will not tolerate any detectable nitrate. Strong protein skimming is thought to be needed for these corals. To help their development, they often need calcium as well as a variety of other nutrients. However, if the circumstances are right, they may grow swiftly and be propagated in the aquarium. The most well-known of these corals is Acropora.
Large-polyp stony corals need less light and water quality than small-polyp stony corals, but they still require extremely low nitrate levels. These corals need feeding in general, although power compact fluorescent lights or numerous regular fluorescents are sufficient for their illumination requirements. The grace coral Cataphyllia jardini, frogspawn, anchor, hammer, and torch corals (Euphyllia species), and golfball corals are among the most popular (Goniopora). There is some evidence that excessive protein skimming may be harmful to these corals, with golfball corals doing particularly badly in well-skimmed aquariums. Some of these corals may need food particles that are removed by aggressive skimming. Again, it is critical to tailor the filtration (and illumination) to the demands of the species being housed.
A few varieties of stony coral live in caves and do not need symbiotic algae or any light at all. The sun corals Tubastrea are the most well-known. These need feeding and should be planted in areas with sufficient water flow since they will suffer if silt builds on them. They also have high standards for water purity.