Small-polyp stony (SPS) corals are among the most diverse and well-known types of corals found in the world’s oceans – they include many specific kinds of corals from the genera Pocillopora, Montipora and Stylophora. Their skeleton is slowly secreted by the epidermis found at the base of each polyp, and as in the case of LPS (large polyp stony) corals, some varieties can grow much faster than others. The beauty and diversity of SPS corals is maintained in stable habitats, where factors such as temperature, alkalinity and water PH are kept between specific values.
Although there is a difference between small-polyp stony corals and LPS corals, there isn’t an actual, concrete distinction between the two. Rather, the transition is smooth, as there are many SPS coral species that have larger polyps, and can often be compared with LPS species. The general difference, however, has to do with the greater fragility and more specific habitat conditions that small-polyp corals may require in order to survive and propagate. In contrast with large-polyp stony corals, they cannot be found at depths where sunlight can’t reach them too easily, nor in waters that are too polluted, murky or cold.
There are many beautiful SPS species that are commonly sought out by divers in tropical regions. These include anything from stunning “flowery” patterns like the ones found on Sunset Montipora, and the vibrant purple stem-shaped polyps of the Booberry Acropora, to incredibly exotic, intricate shapes and multicolored textures, such as in the case of the Bisma Worm Rock. Despite their beauty, SPS corals are quite fragile, being commonly attacked by creatures such as nudibranchs and various insects or flatworms that mainly attack Acropora corals. Also, they require specific habitat conditions, such as a temperature between 72 and 78 F, and moderate to intense sunlight.
Aside from stable temperature and lighting conditions that can usually only be found in the tropics, small-polyp corals also require several other important factors to be just right, before they can survive. The water alkalinity, for example, has to be between 8-12 dKH, while PH fluctuations of only 0.3 (ideal ranges are somewhere between 8.1 and 8.4) can be tolerated, before the corals begin to find it difficult to maintain their life cycles in the long run. Preferred habitats exist in areas like the islands of the Indian and Pacific Oceans, including places like Fiji, the Maldives, Hawaii or Papua New Guinea.
The most well-known varieties of SPS corals include primarily members of Acroporidae, including the Montipora and Acropora genera. These corals are most fascinating, not only due to their remarkable natural beauty and diversity, but also because they are the dominant reef building hard coral species of the world’s oceans. Although their diversity makes them extremely prevalent, like most small-polyp stony corals, these species still require specific conditions in order to thrive and survive, which is part of the reason why they are rarely able to live in deeper waters.