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Acropora cervicornisStaghorn coral

By Krystyn Alter

Geographic Range

Species of the genus -Acropora- are favorable to warm water marine environments. In particular, -Acropora cervicornis- is one of the primary reef building corals in the Caribbean (Birkeland 1997). These species are also located in the Great Barrier Reef of Australia (McGregor 1974).

Habitat

Acropora cervicornis like to live in warm, marine water close to the surface. The tropical western regions of the oceans are where there is most of the coral diversity of coral reef organisms (Birkeland 1997). The polyps that form the coral need tropical waters where the temperatures are higher than 20 degrees centigrade and there is adequate light. They also require a hard surface for which the coral polyps can settle. Staghorn corals, as well as all other corals, need very oxygenated water containing adequate supplies of small planktonic animals. Corals also need clear water, because apart from reducing the light, and heavy rain of sediment would smother them (McGregor 1974)

Physical Description

These corals commonly have tentacles in multiples of three, which is characteristic of all corals belonging to the subclass Zoantharia, also known as Hexacorallia (Encarta 1997). At night, the tiny fingerlike tentacles of the corals emerge. They pump themselves up with water and pop out like tiny stars all over a coral reef (Sargent 1991). The staghorn coral, -A. cervicornis-, grows into "antler-like branches" so the polyps are raised above the sand (McGregor 1974). Staghorn corals have nematocysts, which are stinging cells that are located on their tentacles. These stinging cells are necessary for a coral to obtain food (Sisson 1973).

Reproduction

As in all corals, the Staghorn Coral reproduces both sexually and asexually. The very first stage of reproduction is a sexually-caused stage of reef-building. This occurs when existing polyps expel millions of spermatoza into the water. Some of these gametes are drawn into other polyps that are nearby; the eggs that are produced there are then fertilized and larva develop and float away to produce new polyps. The larva, called planula, are extremely small and bulb-shaped. They are constantly changing shape as they swim/drift (Sisson 1973). They have a mouth at the upper end, which is the wider end with cilia like hairs all over them that are constantly beating and help support them to the surface. The planula that survive predators while floating through the water settle on a suitable hard surface in warm water and attach themselves by spreading out into a disk (Sisson 1973). Once they land here, they begin to secrete a white starlike outer skeleton which permanently cements it to a spot and develop tentacles and grow into mature polyps. Once the first skeletons are built, the founders, or the sexually produced polyps, multiply by asexual methods. Acropora grow branches, which are also known as buds, that become the daughter polyps, which then bud more daughters (McGregor 1974).

  • Parental Investment
  • no parental involvement

Behavior

Staghorn corals as well as many other corals have a very unique symbiotic relationship with algae, in particular the zooxanthellae. These microscopic plants live inside the bodies of all reef-building polyps aiding their growth in an uncertain way. Without these alga, corals grow at 1/10th of the speed and are unable to establish the framework that is necessary for the growth of a coral reef (McGregor 1974). Because the alga need light for photosynthesis, they play an important role in where a coral can live. Carbon is passed by the alga to the coral increasing its energy, and the food caught by the coral may supply nitrogen and phosphorus for both organisms (Encarta 1997).

Food Habits

Staghorn corals use their nematocysts which are located on their tentacles for eating and gaining food. Surprisingly some Acropora species have actually been seen capturing live fish (Sisson 1973). Staghorn corals also eat planktonic animals which float by in the water (McGregor 1974).

Economic Importance for Humans: Positive

Acropora cervicornis house many creatures, some of which may be useful to the medical research field. Some of the species that live in the corals have already yeilded compounds active against inflammations, asthma, leukemia, tumors, heart disease, fungal and bacteria infections, and even viruses including HIV (Chadwick 1999). Staghorn corals are also of vital importance to the stabilization of coastlines, as fish habitats, and for the protection of our biodiversity (Nemoto 1992).

Economic Importance for Humans: Negative

There really are not any negative effects that corals cause to humans. Sometimes they can damage or wreck a boat, but usually they are pretty harmless to humans

Conservation Status

The coral reefs in the eastern tropical Pacific have been most severly degraded by climatic events. Especially after the El Nino of 1982-1983. Many of these reefs have continued to deteriorate since then because coral recruitment has been sparse and sea urchins continue to erode away the framework of the coral. Coral bleaching (loss of zooxanthellae and/or pigment) has been increasingly wide-spread and frequent. In a survey of more than 2,000 sites in the British Virign Islands, it was found that over 95% of Acropora were dead in 1993. (Birkeland, 1997)

Contributors

Krystyn Alter (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

coastal

the nearshore aquatic habitats near a coast, or shoreline.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

native range

the area in which the animal is naturally found, the region in which it is endemic.

radial symmetry

a form of body symmetry in which the parts of an animal are arranged concentrically around a central oral/aboral axis and more than one imaginary plane through this axis results in halves that are mirror-images of each other. Examples are cnidarians (Phylum Cnidaria, jellyfish, anemones, and corals).

threatened

The term is used in the 1994 IUCN Red List of Threatened Animals to refer collectively to species categorized as Endangered (E), Vulnerable (V), Rare (R), Indeterminate (I), or Insufficiently Known (K) and in the 1996 IUCN Red List of Threatened Animals to refer collectively to species categorized as Critically Endangered (CR), Endangered (EN), or Vulnerable (VU).

References

Anonymous, 1997. Coral. Microsoft Encarta. Microsoft.

Birkeland, .. 1997. Life and Death of Coral Reefs. New York: Chapman and Hall.

Chadwick, .. January 1999. "National Geographic" (On-line). Accessed February 15,2000 at http://www.nationalgeographic.com/ngm/9901/fngm/index.html.

McGregor, .. 1974. The Great Barrier Reef: The World's Wild Places/Time-Life Books. Nederland: Time-Life Books International.

Nemoto, .. 1992. Ocean Frontiers: Explorations by Oceanographers on Five Continents. New York: Harry N. Abrams Inc., Publishers.

Sargent, .. 1991. Night Reef. New York: Franklin Watts.

Sisson, .. June 1973. Life Cycle of a Coral. National Geographic, Vol 143 No. 6: 780-793.

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