Acropora
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 A high magnification picture of Acropora. Individual polyps can be seen as dark spots.
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Acropora cervicornis |
Acropora is a genus of coral in the phylum Cnidaria. Depending on the species and location, Acropora may grow as plates or slender or broad branches. Like other corals, Acropora corals are actually colonies of individuals, known as polyps, which are about 2 mm across and share tissue and a nerve net. The polyps can withdraw back into the coral in response to movement or disturbance by possible predators, but when undisturbed they protrude slightly. The polyps usually extend further at night as they capture zooplankton from the water.
These corals have zooxanthellae, symbiotic algae that live in the corals' cells and produce energy for the animals through photosynthesis. Environmental destruction has led to a dwindling of populations of Acropora, along with other coral species. Acropora corals are especially succeptible to bleaching when stressed. Bleaching is due to the loss of the coral's zooxanthellae, which are a golden-brown color. Bleached corals are stark white and may die if new zooxanthellae cannot be assimilated. Common causes of bleaching and coral death include pollution, abnormally warm water temperatures, sedimentation and excess nutrients from runoff.
Acropora genus corals are most common in shallow reef environments with bright light and moderate to high water motion. Many small reef fishes live near acropora colonies and retreat into the thicket of branches if threatened.
Most acropora corals are brown or green but a few are brightly colored and those rare corals are prized by aquarists. Captive propagation of acropora corals is widespread in the reefkeeping community. If given the right conditions, acropora corals grow quickly and individual colonies can exceed 1 meter across in the wild. In a well maintained reef aquarium, finger-sized fragments can easily grow into basketball-sized colonies in 2 to 3 years.
