“At one time,” says Martin, “when many fewer corals were kept with success in reef tanks, it made more sense to use these generic terms to help aquarists understand how to care for a particular coral and which coral may be appropriate for his or her skill level.”
LPS, which stands for “large polyp stony coral (or large polyp scleractinian),” and SPS, which stands for “small polyp stony coral (or small polyp scleractinian),” are hobby-specific terms referring to the size of a coral’s polyp or polyps. In the marine aquarium lexicon, an LPS designation is generally understood to mean “easier to keep,” while an SPS designation suggests the animal is more difficult to keep or an expert-only coral.
“The trouble with these definitions is that there are a number of corals that do not fit readily into either category,” says Martin. He points to various faviids and Goniopora species as examples of hard to classify corals when using the LPS-SPS designation.
As Daniel Knop, the international editor of Coral Magazine and author of Successful Reef Aquarium, pointed out in an interview with Blue Zoo News, “The category LPS was basically created by reef aquarists trying to group those corals that can be kept in a reef tank, in contrast to those small-polyp scleractinians (SPS) that were not able to survive in an aquarium back in the eighties,” said Knop. “As we know now, the LPS survived back then mainly because they die slower, while SPS die very quickly.”
Knop does have his own working definition of LPS and SPS corals—he sets the point of differentiation at a corallite diameter of four centimeter (roughly 1.5 inches)—but he suggests what we here at Blue Zoo do when it comes to making a purchasing decision. In short, do your genera (or species-specific) research before purchasing any coral. “While the terms LPS and SPS are a good starting point for the hobbyist considering a coral for his or her tank,” says Martin, “we encourage everyone to dig a little deeper into the specific husbandry needs of the actual animal being considered.”
Every reef keeper should have several coral reference books in his or her library (e.g.,Aquarium Corals by Eric Borneman and Corals: A Quick Reference Guide by Julian Sprung). In addition, fellow reefers at club meetings, conferences or online are great resources. “You also can always email or call us,” says Martin. “At Blue Zoo, we believe the educated hobbyist is the best hobbyist, and we’d be happy to help you in any way we can.”
Some Important Terminology
Polyp: A polyp is the individual unit of all corals. It is often cylindrical or tube-like in shape with a “foot end” (called the aboral surface) and a “mouth end.” The foot end is either attached directly to substrate by way of a pedal disc, or, in the case of colonial colonies, it is attached to other polyps by way of a mat or a thin layer of tissue called the coenosarcs, which covers the skeleton. Tentacles surround the mouth, and the tentacles are armed with stinging cells called nematocysts that assist in food capture, competition with adjacent corals and defense. The size of the polyp has often been linked to ease of care in the reef aquarium hobby, although this is not always the case.
Scleractinia: Scleractinians are marine animals commonly called stony corals. They possess a hard (or “stony”) skeleton the animal builds by depositing aragonite (made from calcium carbonate the polyp obtains from the seawater) into cup-shaped structures calles corallites.
Corallite: The corallite is the cup-like skeleton made by a coral polyp. To measure the corallite diameter, one measures from one wall of the corallite across to the other. The blades standing up inside the corallite are known as septa. The septa are called costae outside the corallite walls.