Cup corals are a group of marine invertebrates classified as stony corals, known for their distinct, cup-like skeletal structures. These organisms belong to the phylum Cnidaria and the class Anthozoa, making them relatives of sea anemones and jellyfish. While they may appear plant-like, cup corals are indeed animals that construct a rigid framework of calcium carbonate, providing a foundation for their soft polyps.
Unique Biological Traits
Unlike many well-known reef-building corals that form vast, interconnected colonies, most cup corals live as solitary individuals. Each polyp, which can reach up to 10 centimeters in diameter, develops its own calcareous cup, though multiple polyps may sometimes form small, clustered groups.
Cup corals are ahermatypic, meaning they do not contribute to reef building. This classification stems from their lack of symbiotic algae, known as zooxanthellae, within their tissues. Consequently, these corals do not rely on sunlight for energy production through photosynthesis, allowing them to inhabit environments where light is scarce.
Their independence from sunlight dictates a different feeding strategy; cup corals are active carnivores. They extend their translucent tentacles in dim conditions to capture food particles from the water column. Their diet primarily consists of zooplankton, small crustaceans, and other small organic particles.
Habitat and Distribution
Cup corals thrive in diverse marine environments inaccessible to photosynthetic corals. Since they do not require sunlight, these corals are frequently found in deep waters, on the ceilings of caves, and beneath overhangs where light penetration is minimal. Depths can range from a few meters to over 1,000 meters, depending on the species.
Their distribution spans globally, inhabiting both tropical and temperate waters across the Indo-Pacific, Red Sea, Atlantic, and Mediterranean regions. Cup corals also colonize man-made structures, including shipwrecks, offshore oil rigs, and pier pilings.
These environments feature moderate to strong water flow, which is beneficial for cup corals as it continuously brings them a supply of food particles. Their presence on such structures can sometimes influence local marine ecosystems, particularly in areas where they are introduced as non-native species. Their resilience allows them to occupy niches that other coral species cannot.
Caring for Cup Corals in Aquariums
Keeping cup corals, often called Sun Corals or Orange Cup Corals in the aquarium hobby, demands consistent attention. Their non-photosynthetic nature means they cannot sustain themselves from aquarium lighting, making direct and regular feeding necessary for their survival.
Target feeding is the most effective method, involving the direct delivery of meaty foods to each individual polyp. Suitable food items include small frozen mysis shrimp, enriched brine shrimp, or finely chopped marine seafood. Feeding should occur frequently, ideally daily or at least three to four times a week.
Regarding placement within an aquarium, cup corals prefer areas with moderate to strong water flow, which helps deliver food and remove waste. They do not need intense light; placing them in lower-light areas or under overhangs can mimic their natural shaded habitats. Maintaining stable water parameters, including calcium levels around 400-450 ppm for skeleton growth, is important.