The allure of a thriving marine aquarium often brings to mind vibrant coral reefs bathed in intense sunlight. However, a captivating underwater world can also be created with corals that flourish in more subdued lighting conditions. These corals offer a unique aesthetic, providing deeper hues and intriguing forms. Their ability to thrive without strong illumination makes them an appealing choice for many aquarists.
What Defines Low Light Corals
Low light corals possess adaptations that enable them to prosper in environments with reduced light availability. Their survival relies on a symbiotic relationship with zooxanthellae, microscopic algae within their tissues. These zooxanthellae perform photosynthesis, converting light into energy for the coral host.
In lower light settings, the zooxanthellae in these corals are adapted to efficiently capture and utilize available light. Some low light corals also host photosynthetic pigments that absorb specific light wavelengths penetrating deeper water. This allows them to maximize energy production even when light intensity is diminished.
Structural adaptations also aid these corals. Many exhibit plate-like, encrusting, or branching growth forms that increase their surface area. This expanded surface allows greater exposure to scattered or indirect light, optimizing photon capture.
Beyond light-harvesting, some low light corals supplement nutrition through heterotrophic feeding. They may capture small planktonic organisms or absorb dissolved organic matter from the water. This dual strategy provides an alternative energy source, reducing reliance on light.
Popular Low Light Coral Species
Several coral species are well-suited for aquariums with lower light levels, offering diverse appearances and forms. Mushroom corals, soft corals with a disc-like shape, come in various colors and textures. They are excellent beginner corals due to minimal light requirements.
Another popular choice is Large Polyp Stony (LPS) corals. Blastomussa corals, or blastos, have colorful, fleshy polyps and do well in low to moderate light. Candy Cane corals (Caulastrea furcata), also known as Trumpet or Bullseye corals, display bright colors despite modest light needs, thriving in 50-150 PAR.
Several other species are also popular:
- Chalice corals (Echinophyllia sp.): Slow-growing, hardy LPS corals forming plates or encrusting rockwork. They come in various colors and patterns, suitable for low light areas, generally requiring 50-100 PAR.
- Duncan corals: Another hardy LPS option, presenting in shades of green and blue, and can thrive even at PAR levels as low as 50.
- Green Star Polyps (GSP): Fast-growing soft corals with waving polyps that add vibrant color and movement. They prefer low light, particularly blue light.
- Xenia polyps: Often called “pulsing” Xenia, these soft corals have rhythmic pulsing polyps that do best in low to medium light.
Essential Care for Low Light Corals
Successful maintenance of low light corals involves careful attention to environmental parameters. While they tolerate lower light, illumination is necessary for photosynthesis. Aim for PAR levels generally between 30 and 150, depending on the species. Soft corals typically thrive at the lower end (30-50 PAR), and some LPS corals do well up to 150 PAR. LED fixtures with adjustable intensity and spectrum are preferred, allowing precise control over the light environment.
Water parameters are also important. Maintain stable water temperature between 75-80°F (24-27°C) and salinity at 1.025-1.026 specific gravity. Maintain alkalinity within 8-12 dKH, calcium at 400-450 ppm, and magnesium at 1250-1350 ppm. Regular testing and consistent dosing or water changes help maintain these parameters.
Water flow is another consideration; most low light corals prefer low to moderate flow. Strong, direct flow can damage tissues. Gentle, indirect flow helps deliver nutrients and removes waste without causing stress. Placement within the aquarium should account for both light and flow, often in the lower or shaded areas of the tank.
Feeding strategies can complement the energy derived from light. While some low light corals primarily rely on zooxanthellae, many benefit from supplemental feeding. Offering broadcast feeds of phytoplankton or zooplankton, or target feeding individual polyps with specialized coral foods, enhances growth and coloration. This additional nutrition helps corals compensate if light levels are at the lower end of their acceptable range.