Hump Coral

Porites lobata is a hermatypic or reef-building coral. It varies greatly in size and shape depending on its environment. On wave-exposed reef slopes it is encrusting whereas in calm water areas it can grow into large helmet-shaped or hemispherical hummocks up to 6 metres (20 ft) high and wide. Growth rates are very slow, sometimes being as little as 1 centimetre (0.39 in) per year, and this means that large corals are very old. The general colour is greenish, yellow or tan because of the zooxanthellae, single-celled microalgae, that live symbiotically within the tissues. These make organic nutrients available to the polyps through photosynthesis. The corallites are very small and closely packed. They are joined directly to one another by fused but porous walls and have diagnostic skeletal characteristics that are only visible under the microscope. The septa are also fused. The polyps are 1 millimetre (0.04 in) in diameter and the coenosarc covering the skeleton is thin.

Porites lobata is a common species of coral and is found in the tropical parts of the Indian and Pacific Oceans. The range extends from East Africa, the Red Sea and the Gulf of Aden, through Indonesia and Australian waters to the Pacific coasts of Gulf of California and Central America. It is the most common coral species in Hawaii. It is often the dominant species on reef margins, in lagoons and on fringing reefs at depths down to 30 metres (98 ft). It occurs in a slightly deeper zone than cauliflower coral.

Porites lobata forms part of the coral reef biome. Several fish species live among the lobes of the coral, some sheltering there and others, like the puffer fish (Arothron meleagris) grazing on the polyps. The snapping or pistol shrimp (Alpheus deuteropus) is a commensal and lives among the lobes where it may form grooves and tunnels.