Cyphastrea agassizi

Cyphastrea agassizi is a colonial stony coral in the family Merulinidae, forming encrusting to massive colonies with small, closely spaced corallites. Like other scleractinian corals, it builds a calcium carbonate skeleton through the combined action of coral polyps and their symbiotic algae (zooxanthellae), which supply the coral with photosynthetic energy in exchange for shelter. Polyps extend at night to capture plankton, supplementing the nutrition gained from their algal symbionts.

As a reef-building species, it contributes to the structural framework of coral reefs, providing habitat complexity that supports fish and invertebrate communities.

This species inhabits shallow marine reef environments across the western and central Pacific and parts of the Indian Ocean, with recorded populations in Japan, the United States, Australia, the Cocos (Keeling) Islands, the Marshall Islands, U.S. Outlying Islands, Malaysia, and the Philippines. It typically occurs on reef flats and slopes in clear, shallow waters.

The species is threatened by rising sea temperatures, which trigger coral bleaching by disrupting the coral-algae symbiosis, and by ocean acidification, which reduces the availability of carbonate ions needed for skeletal growth. Coastal development introduces sediment runoff that smothers colonies and reduces light penetration, while destructive fishing methods and boat anchor damage cause direct physical harm to reef structures.

Conservation efforts include reef monitoring programs, marine protected areas within parts of its range, and international trade regulation. Its listing as Vulnerable under the IUCN Red List highlights ongoing conservation concern. Population trends remain unknown due to limited targeted survey data.

Given the persistence of warming, acidification, and localized human pressures, the species' long-term outlook depends heavily on broader climate mitigation and reef management measures.

Lesser knob coral inhabits shallow coral reef environments in the Indo-Pacific, typically found on reef flats and lagoons at depths of 1-20 meters. It forms encrusting colonies on hard substrates in areas with moderate water flow and good light penetration.