Seriatopora hystrix

Seriatopora hystrix, known as thin birdsnest coral, is a colonial stony coral from the family Pocilloporidae. It grows in tangled, bushy clumps of slender, tapering branches with pointed tips, which can reach about a yard across.

In shallow areas with strong water movement, the branches are thicker than in deeper or sheltered spots. Its corallites form neat rows of oval, cup-like depressions with raised rims; polyps emerge at night. Colors include cream, pink, yellow, brown, or blue.

Distribution and habitat

This coral is native to a wide Indo-Pacific range, from East Africa, Madagascar, and the Red Sea through the Indian Ocean to tropical Australia, Japan, the South China Sea, and island groups in the West and Central Pacific. It grows on reefs and reef flats, mostly between 3 and 15 meters deep. The type locality is the Fiji Islands.

Ecology

Reproduction is both sexual and asexual. As a hermaphrodite, mature polyps produce sperm and eggs. Sperm are released into the water and drawn into other polyps of the same or nearby colonies; larvae are brooded inside the mother. Self-fertilization may be important.

Larvae settle within about 24 hours, suggesting limited dispersal—many settle within tens of meters of the parent, though some may travel farther in warm currents. The coral hosts symbiotic dinoflagellates (Symbiodinium) in its tissues, which are transferred during brooding; different Symbiodinium species associate with it in different parts of its range, likely an example of coevolution and specialization. Asexual reproduction occurs when broken fragments form new colonies in suitable spots.

Under stress, "polyp bail-out" can happen: the living tissue (coenosarc) isolates a polyp, which detaches, settles, and grows a new skeleton. In the lab, about 5% of such polyps survived to found new colonies. This coral has a high growth rate, high reproductive output, and short lifespan, often being the first scleractinian coral to colonize disturbed areas.

Its bushy form provides habitat for other animals. Symbiotic decapod crustaceans find shelter and food (mucus) there.

Two species of alpheid shrimp and three species of xanthid crab are thought to be obligate symbionts, found only on this coral. These crustaceans may attack predators, benefiting the coral. A single colony usually houses one species of symbiotic crustacean (adults and juveniles), but large colonies may host two.