Many people who choose a marine aquarium choose a reef aquarium. That is, an aquarium with fish and live corals. The range of corals is large and diverse. Below is a global overview of the types of corals.
Corals are still often seen as plants, but in fact they are animals. They often have a mouth, a stomach, sexual organs and a more or less developed nervous system. The common corals in the aquarium can be roughly divided into two groups. The soft corals and the stony corals.
Soft corals
The difference between the soft corals and the stony corals is that soft corals do not have a calcium carbonate skeleton. They pump up their tissue with water to get up. The largest group within the soft corals is represented by the leather corals. These corals feel leathery. Characteristic of this type of corals is that they shed occasionally. They then get a slimy layer over them that slowly comes off. In this way the corals liberate themselves from waste that has ended up on their tissue. Leather corals are usually brown or beige in color. A few varieties are known with a green fluorescent color. Leather corals are generally easy to keep and are not aggressive towards other corals, unlike many stony corals. They require less light and also impose less stringent water quality requirements than many stony corals. In addition to leather corals, the group of soft corals also includes crusting corals such as buttons and star polyps. Crust-forming corals are generally easy to keep, just like leather corals. They need light to grow, but don’t require as much light as stony corals.
Stony corals
Stony corals get their name from the hard skeleton of calcium carbonate. These corals require a high level of calcium in the water so that they can build their skeletons. The stony corals are divided by aquarium keepers into small polyp stony (sps) corals and large polyp stony (lps) corals. Lps corals often have larger polyps and are not entirely dependent on light because they absorb food from the water. Many of these species need targeted feeding. The sps corals usually have smaller polyps than the lps corals. They cannot absorb large pieces of food from the water and mainly live from light. These species have the highest demands in terms of water quality and lighting. Both lps and sps corals often have tentacles with which they damage other corals in the vicinity by means of nettle cells.
Gorgonians
A coral species that cannot actually be classified in one of these two groups is the gorgon. Gorgons often look like soft corals, as they often rock back and forth in the current. However, these corals have a fairly solid skeleton of lime particles and ‘gorgine’ a horn-like protein substance. This makes the gorgonians a separate category. Gorgons are generally not that easy to keep. Many gorgonians are food specialists, but it is not well known what exactly they need. Most gorgonians are believed to consume little plankton, unlike many other corals.
This description is very brief and is only intended to represent a global distinction.