Hard corals are also referred to as stony corals, and are members of the order Scleractinia. Hard Corals can be differentiated from other types of corals by their calcium skeleton or base. These corals are often broken down into two groups by their polyp type: small polyp stony corals (SPS) and large polyp stony corals (LPS). Live corals are found throughout the world in tropical waters on coral reefs. Most of these corals are found at depths no greater than 50 metres.
Hard corals are similar to anemones in that both animals use a mechanism called a nematocyst to deliver a sting to ward off predators, or maintain their space on the reef from other species of competing corals. Some species of LPS have sweeper tentacles that can reach several inches long at night. These tentacles will sting adjacent and neighboring corals causing extensive damage to some species. Do not touch hard corals as damage to the coral will usually occur. Hard corals reproduce both sexually by releasing eggs and sperm into the water, and also asexually by producing buds generated from the parent.
Most hard corals obtain nutrients from the symbiotic algae zooxanthellae contained within their bodies. Corals and algae have a special relationship. Coral receives nutrients and oxygen from algae, and the algae receives carbon dioxide and nutrients from the coral. When recordingMussimilia spp. only count individual colonies. Record presence of large colonies and indicate position (GPS) and depth on reef.