Pohnpei-Between Time & Tide . The Coral Reef

The Coral Reef

oral is created by colonies of small animals called polyps, related to sea anemones and other cnidarians. Polyps extract calcium carbonate from seawater to form a hard, exoskeletal structure around themselves. To begin building, coral polyps need a substrate on which to attach themselves and warm tropical waters that are shallow and clear enough to be penetrated by sunlight. Reef corals typically require waters that range in temperature from 18ºC to 29ºC to survive. They are also sensitive to salinity levels. Corals will not grow where salinity is less than about 27%, such as near river mouths or other sources of freshwater. The polyps themselves generally feed at night on microorganisms in the water. During the day, A Coral Variety

they recoil and only their hard coatings are visible. Over time, older reef becomes essentially coral limestone. New polyp growths germinate on the old layers, building up and outward.

Tropical corals can grow between 0.4 and 2 inches in a year. Reductions in ocean clarity, heavy silt deposition and human pollution can slow or eliminate reef growth, resulting in the destruction of the many varieties of animals that live and depend on the reef. Mangrove swamp forests, which skirt the island's coastline, are essential in protecting lagoon reef from freshwater run-off and accompanying debris that can foul the water, block sunlight and ultimately smother the reef. Pohnpei's waters have a wide variety of thriving corals. Among these, are staghorn and elkhorn fire corals, mushroom coral, table coral and brain coral. Fire corals have nematocysts (stinging cells) on their points which can cause a temporary burning skin irritation if touched.

CIGUATERA POISONING

Reef fish can be potentially dangerous to eat, if affected by ciguatera poisoning. Ciguatera is caused by Gambierdisus toxicus, a dinoflagellate that is believed to reside on some tropical seaweeds. Drastic disturbances in the ocean system, caused by typhoons or human processes, seem to bring about outbreaks. Fish that have ingested G. toxicus are poisonous to humans. Ciguatera symptoms include headaches, nausea, irregular pulse, reduced blood pressure, fever---and in some cases, convulsions, paralysis or death. To reduce the chances of ciguatera poisoning, fish where the locals do. If you buy fish, have a knowledgeable local inspect it before eating.

BLUE CHROMIS (Chromis cyanea) schools create a metallic blue halo around many large coral heads in Pohnpei's lagoon.

Text by Alex Zuccarelli 2003.
Image/Photo credits: Coral image courtesy of Shell Horizons©. Girls with groupers photo courtesy of Daniel Moor ©2000-01. Chromis photo courtesy of Anthony Jones ©1997-2000. Gallery; 3 courtesy of Daniel Moor ©2000-01, 8-10 courtesy of Daniel Moor ©2000-01. All other photos, images and maps property of Alex Zuccarelli.
All photographs on this page were used with the written permission of their perspective owners, except where otherwise indicated.

Primary Sources

Ashby, Gene
1993. Pohnpei: Island Argosy. Rainy Day Press: Eugene.
Castro, Peter & Michael E. Huber
2000. Marine Biology, 3rd Edition. McGraw Hill.
Cousteau, Jacques-Yves
1971. Life and Death in a Coral Sea. Doubleday & Company, Inc.: Garden City.
Darwin, Charles
1897. The Structure and Distribution of Coral Reefs. D. Appleton & Company: New York.
Duxbury, Alyn C., Alison B. Duxbury & Keith A. Sverdrop.
2000. An Introduction to the World's Oceans, 6th Ed. McGraw-Hill Companies, Inc.
Fischer, John L.
1957. The Eastern Carolines. Pacific Science Board: New Haven.
Levy, Neil M.
1996. Micronesia Handbook. Moon Publications, Inc.: Chico.
Longhurst, Alan R. and Daniel Pauly
1987. Ecology of Tropical Oceans. Academic Press, Inc.: San Diego.
Merlin, M., D. Jano, W. Raynor, T. Keene, J. Juvik & B. Sebastian
1992. Tuhke en Pohnpei (Plants of Pohnpei). Department of Education, Pohnpei State, Office of Historic Preservation, FSM & Environment and Policy Institute, East-West Center, University of Hawaii.

On-Line Resources