Trachyphyllia geoffroyi, the open brain coral, is a classic large‑polyp stony coral (LPS). Adults are often free‑living on sand or rubble in lagoons and back reefs (juveniles may begin attached, then detach later). It hosts zooxanthellae (Symbiodiniaceae), relying on photosynthesis by day and extending feeding tentacles at night to capture micro‑zooplankton and particulates.
Ecology & Biology
Nutrition: primarily photosynthesis; nocturnal particulate/zooplankton feeding through the oral disc.
Growth form: typically a single large polyp (solitary colony) that can move slightly over sand as currents shift.
Reproduction: sexual broadcast spawning/planulation alongside asexual budding/fission of skeletal pieces.
Identification
Skeleton forms crescent to ring‑like valleys and ridges; the fleshy oral disc swells markedly by day. Colours include greens, reds, orange‑reds, pinks and “rainbow” combinations, with conspicuous radiating septa lines. Unlike meandroid “brain corals”, this species is solitary rather than composed of connected valleys.
Size & Longevity
Expanded diameter: typically 8–20 cm; up to 25–35+ cm under favourable conditions.
Thickness: robust skeleton and tissue; at night tissues deflate exposing hard ridges.
Life: long‑lived reef builder, persisting for many years to decades on stable reefs.
Range & Habitat
Widespread across the tropical Indo‑Pacific (Indian Ocean to W. Pacific, SE Asia, northern Australia). Common on lagoons, back‑reefs and upper outer‑reef zones over sand/rubble at ~3–30+ m, favouring moderate light and gentle–moderate flow while avoiding heavy sediment.
Threats & Conservation
Thermal stress & bleaching during heatwaves.
Sedimentation/pollution reducing photosynthesis and promoting disease.
Collection/trade—requires regulated practices; aquaculture/fragmentation can reduce wild harvest.
IUCN: assessments vary among sources; for consistency here we mark it as Not Evaluated (NE). Priorities: protect healthy reef tracts, manage nutrients/sediments and regulate tourism/trade.
