Ten-ray Star Coral

The Ten-ray Star Coral (Madracis decactis) is a small, stony coral species recognized by its distinctive star-shaped corallites, most commonly bearing ten septa arranged in a radial pattern, which give the species its common name. Colonies form encrusting to knobby mounds in shades of brown, tan, or greenish-yellow, contributing structural complexity to reef habitats across the tropical Atlantic, including the Caribbean, Gulf of Mexico, Brazilian coast, and mid-Atlantic island systems such as Ascension and St. Peter and St.

Paul Archipelago. It typically inhabits shallow to mesophotic reef zones, attaching to hard substrates where light penetration supports its symbiotic relationship with zooxanthellae algae. The species is currently classified as Critically Endangered (CR) by the IUCN, with a decreasing population trend driven by cumulative reef stressors.

Rising sea surface temperatures have triggered repeated mass bleaching events, weakening colonies and reducing reproductive output, while ocean acidification compromises skeletal calcification necessary for growth and reef-building. Disease outbreaks, sedimentation from coastal development, and localized pollution further degrade the shallow-water habitats this species depends upon. Populations in the Caribbean and Brazilian reef systems have shown particularly steep declines, mirroring broader basin-wide coral loss.

On a more encouraging note, Madracis decactis populations in more remote sites, such as the mid-Atlantic ridge islands, appear comparatively resilient due to lower direct human pressure, and researchers view these isolated colonies as important genetic reservoirs for future restoration work. Marine protected areas established around several of its range states now restrict fishing and anchoring activity near reef structures, and ongoing coral monitoring programs are helping scientists track bleaching resilience traits that could inform selective restoration efforts. Continued research into thermal tolerance among surviving colonies offers a genuine pathway toward safeguarding this ecologically important reef-building species.

Madracis decactis inhabits shallow coral reef environments in the Caribbean, typically found at depths of 1-20 meters on reef slopes and fore-reef areas. This branching coral species prefers clear, well-circulated waters with moderate to high wave energy and forms small colonies on hard substrates.