Acropora tenuis is a visually striking species of stony coral, known for its diverse forms and vibrant colors. This small polyp stony (SPS) coral holds significance in marine ecosystems, contributing to the structural complexity of reefs. Its popularity extends to the aquarium hobby, where enthusiasts often seek to cultivate its beauty.
Physical Characteristics
Acropora tenuis colonies grow in dense, bushy, or corymbose clumps, sometimes resembling a tabling form. Branches often grow close together, forming ball-like shapes or encrusting rockwork. Individual axial corallites are distinct and tubular, while radial corallites are arranged in a neat rosette pattern with slightly flaring lips.
This species exhibits many vibrant colors, including blue, yellow, green, cream, and purple. The branch tips often display contrasting colors, such as purple or blue, which can be more pronounced under specific lighting. These growth patterns and colorations assist in identification.
Natural Environment and Ecological Role
Acropora tenuis thrives in shallow, clear, and high-energy reef environments, including upper reef slopes, crests, and flats. Its geographical distribution spans the Indo-Pacific region, including the Indian Ocean, western Pacific Ocean, Red Sea, Gulf of Aden, Australia, and Japan. These corals flourish in warm, tropical waters where strong water movement provides a flow of nutrients and oxygen.
This coral is a reef-building species, contributing to the formation and growth of underwater structures. The intricate colonies of Acropora tenuis create diverse habitats, offering refuge and nursery grounds for many marine species, from fish and invertebrates to sea turtles. Its presence is an indicator of overall reef health, as its sensitivity to environmental changes reflects the well-being of the broader ecosystem.
Aquarium Care and Propagation
Cultivating Acropora tenuis in a home aquarium requires stable environmental parameters. Water temperature should be maintained between 75-80°F (23.9-26.7°C), with stability (ideally within 0.5°F) being important. Salinity should be 1.025-1.026 specific gravity.
Alkalinity is a sensitive parameter, with a recommended range of 8-12 dKH, though some aquarists find success between 7-8 dKH. Calcium should be 400-450 ppm, and magnesium between 1250-1400 ppm, as these are needed for skeletal growth. High Photosynthetically Active Radiation (PAR) levels (200-400) are necessary for photosynthesis, supported by intense lighting from metal halides or high-output LEDs.
Moderate to strong, random, indirect water flow is also required to deliver nutrients, remove waste, and encourage polyp extension. While Acropora tenuis primarily obtains energy through photosynthesis via symbiotic zooxanthellae, supplemental feeding with SPS-specific coral foods, phytoplankton, or zooplankton 2-3 times per week can encourage faster growth and better polyp extension. Propagation is commonly achieved through fragging, where small pieces are cut and attached to new substrates.
Conservation and Threats
Acropora tenuis is listed as “Near Threatened” on the IUCN Red List, with its population decreasing. It faces threats in the wild, largely from global climate change. Rising ocean temperatures contribute to mass coral bleaching events, where corals expel their symbiotic algae, leading to stress and often mortality.
Ocean acidification, a consequence of increased atmospheric carbon dioxide, reduces carbonate ions needed for skeletal growth. Disease outbreaks, such as white-band disease, also pose a risk, particularly when corals are stressed from environmental changes. Habitat destruction from human activities like dredging and land reclamation diminishes suitable environments. It is also susceptible to predation by organisms such as the crown-of-thorns starfish.