What is a coral?
Corals are animals. They inhabit oceans and seas and are the builders of our coral reefs. They can be divided into three groups: SPS (Stony corals & our reef builders), Soft corals, and LPS (Large Polyp Stony) corals which are a little bit of both SPS and soft corals in regards to physical characteristics. Corals are in the Phylum Cnidaria and in the class Anthozoa.
SPS corals are the reef building corals. Normally branching or plated these stony corals have small polyps extending from a hard skeleton. As the coral grows it uses calcium from the water it lives in to extend its limestone body. New polyps form on this extension and the coral continues to grow, similar to leaves sprouting from a new branch on a tree. If the coral should die for any reason, the hard body is left behind where new corals will build on top of it. Over millions of years a reef is formed through this process. SPS corals feed mainly through a symbiotic relationship with an algae called zooxanthellae. This algae is found living in the polyps of the SPS corals and feeds the coral (photosynthetic). In regards to the reef keeping hobby SPS corals are normally considered more of an advanced coral to keep. You can view some of the different SPS coral articles here.
LPS corals or Large Polyp Stony corals are much fleshier than SPS corals but still produce a hard skeleton which they sprout from , when the coral dies it still contributes to the coral reef. The skeleton is formed in the same way by absorbing calcium from the water. While many LPS have a symbiotic relationship with zooxanthellae some are non-photosynthetic species and rely on catching food in their tentacles for survival. In most cases even if a LPS species is photosynthetic it will still have the ability to trap food and ingest it. If you choose to keep LPS corals in your personal reef it is important to realize that some of these animals will need to be directly fed and some are considered to be aggressive to other corals. They range from beginner corals all the way up to advanced corals for the salt water aquarium hobbyist. Click here if you would like to read about different LPS species for the reef aquarium.
Soft corals are found worldwide. They lack the hard skeletons found in both SPS and LPS corals, instead for the most part they have fleshy or leathery bodies. Their growth rates are typically far faster because of this. Many soft corals are planktivores; this means they are basically filter feeder either on phyto-plankton or zoo-plankton. They require strong currents to wash food through their tentacles and carry away the waste. These corals are typically the easiest to keep in a reef aquarium and make great starter corals for the beginning salt water aquarist. They are also generally less expensive. If you would like to read more about different soft coral species click here.