Millepora tenera

Millepora tenera is a colonial hydrozoan commonly known as a fire coral, despite its coral-like appearance and reef-building role. Unlike true stony corals, it belongs to Class Hydrozoa and constructs calcium carbonate skeletons through colonies of tiny polyps that also possess stinging cells capable of delivering a painful sting to predators and unwary divers. These colonies form encrusting, branching, or plate-like structures depending on local conditions, contributing to reef framework complexity and providing habitat for other reef-associated organisms.

As a photosynthetic-symbiont host, it relies on zooxanthellae for much of its energy, similar to reef-building corals.

The species occurs across the Indo-Pacific region, with records spanning Papua New Guinea, the Solomon Islands, American Samoa, the Philippines, Madagascar, Micronesia, Australia, Indonesia, Thailand, Vietnam, Yemen, Japan, and Fiji. It inhabits marine neritic zones, typically on shallow reef flats and slopes within photic depths suitable for its symbiotic algae.

Millepora tenera is classified as Endangered, with a decreasing population trend. Key threats include problematic native species and disease outbreaks, which can cause tissue loss and colony mortality, along with ongoing habitat shifting and alteration linked to changing reef conditions, including temperature-driven disturbances and shifts in benthic community structure. These pressures compound the general vulnerability of reef-building organisms to environmental change.

Conservation efforts rely primarily on broader marine protected area networks across its range states, along with reef monitoring programs that track coral community health, including hydrozoan components often overlooked in coral-focused surveys. No species-specific recovery programs are documented. Given ongoing habitat degradation and disease pressures across its range, the species' trajectory remains one of continued decline absent significant reductions in reef stressors.