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PROMOTING THE HEALTH AND SUSTAINABILITY OF HAB I TATS U.S. Coral Reefs—Imperiled National Treasures

Coral reefs are home to 25% of all marine species. How- ever, the tiny colonial animals that build these intricate limestone masses are dying at alarming rates. If this trend continues, in 20 years the living on many of the world’s reefs will be dead, and the ecosystems that depend on them severely damaged. As part of the effort to protect our Nation’s extensive reefs, U.S. Geological Survey (USGS) scientists are working to bet- ter understand the processes that affect the health of these ecologically and economically important ecosystems.

In recent decades, many of the world’s coral reefs have been severely damaged by both natural processes and human activities. The reasons for the catastrophic decline in the health The beauty and abundance of life in habitats, like this one in , attract a variety of visitors, of these complex marine ecosystems including sport divers and recreational fi shermen. Such activities in U.S. waters alone generate billions of dollars a year for the tourist industry. (Copyrighted photograph courtesy of Sandra Edwards.) are poorly understood. Coral reefs are home to 25% of all marine species, and it is crucial that they be protected. To preserve and protect the biodiver- is a cooperative effort among Federal Coral reef habitats contribute hundreds sity, health, and social and economic agencies, state agencies, and academic of millions of dollars annually to the value of coral reef ecosystems in the institutions and is co-chaired by the U.S. fishing industry and help United States and its territories, the U.S. Secretaries of Interior and Commerce. generate billions of dollars a year for Coral Reef Task Force was established by There are extensive coral reefs in the the Nation’s tourist industry. Executive Order in 1998. The task force waters of the United States and its ter- ritories, covering more than 4 million A large school of jacks swims in acres of the sea fl oor in the Atlantic Poka‘i Bay, O‘ahu, Hawai‘i. Coral reefs in Hawai‘i and elsewhere pro- Ocean, Gulf of Mexico, Caribbean Sea, vide shelter and nursery grounds for and the Pacifi c Ocean. More than 60% of many commercially and culturally the Nation’s coral reefs are found in the important species of fi sh and inverte- brates. Such reef habitats contribute extended Hawaiian Island chain. Most hundreds of millions of dollars a of these are included in the recently des- year to the United States fi shing ignated Northwestern Hawaiian Islands industry. (Photograph courtesy of National Oceanic and Atmospheric Coral Reef Reserve, the largest U.S. Administration/James P. McVey.) nature preserve.

U.S. Department of the Interior USGS Fact Sheet 025–02 U.S. Geological Survey 2002 Extensive coral reefs are found in the waters of the United States U.S. CORAL REEFS and its territories. In the Atlantic Ocean, Gulf of Mexico, and the Caribbean Sea these include reefs off Florida, , , and the U.S. Virgin Islands. 0 300 MILES In the Pacifi c Ocean, they N UNITED STATES 30° 0 300 KILOMETERS include those of the Hawaiian Islands, , Johnston FLOWER ATLANTIC OCEAN , the Northern Marianas, GARDEN Saipan, , Kingman Reef BANKS FLORIDA REEF and , Howland TRACT Island, , Jarvis Gulf of Mexico U.S. VIRGIN 20° N Island, and American . CUBA ISLANDS More than 60% of the Nation’s PUERTO Corals are marine animals related to jellyfish and coral reefs are found in the ex- RICO anemones. Coral polyps, the individual animals MEXICO tended Hawaiian Island chain. Caribbean Sea that make up both colonial and solitary corals, catch plankton (microscopic plants and animals) EXTEND 30° N ED H and other suspended food particles with arm-like AWA IIAN MIDWAY IS LA tentacles, which feed a centrally located mouth. ISLAND ND C HA Coral reefs are formed by colonies of “hard” corals IN NORTHERN WAKE ISLAND that secrete calcareous exoskeletons, giving them MAIN MARIANA ASIA HAWAIIAN ISLANDS structural rigidity. (Photograph courtesy of Florida JOHNSTON ISLANDS Keys National Marine Sanctuary.) SAIPAN ATOLL GUAM KINGMAN REEF AND PALMYRA ATOLL centrally located mouth. Most hard corals also host symbiotic algae, a long-standing BORNEO 0° BAKER ISLAND JARVIS and successful partnership. These algae ISLAND provide them with an additional food source through photosynthesis. Coral reefs are formed by corals that 0 900 MILES AMERICAN secrete hard calcareous (aragonite) exo- SAMOA 0 900 KILOMETERS skeletons, giving them structural rigidity. These colonial “hard corals” form elabo- rate fi nger-shaped, branching, or mound- What is a reef? a reef to rigid biological constructions that shaped structures and can create masses The word “reef” has different meanings have formed in shallow water. of limestone that stretch for tens or even to different people. To a mariner, the term The Earth’s fi rst reefs were built by hundreds of miles. “reef” applies to shallowly submerged nav- photosynthesizing cyanobacteria about Although corals have a wide distribu- igational hazards. To a surfer, a reef is an 2.5 billion years ago. From fossil remains, tion in the world’s oceans, the varieties undersea obstruction that can make waves it is known that a variety of organisms that form reefs are typically restricted (and surfboards) break. Geologists and bi- have constructed reefs, including bivalves to relatively shallow, warm tropical wa- ologists generally restrict the defi nition of (clams and oysters), bryozoans (coral-like ters between latitudes 30° north and 30° animals), and sponges. south. Clean, clear water is essential to To scientists the word “reef” refers to rigid bio- Corals have been found their health. Once coral larvae settle on logical constructions that in fossil reefs as old as a hard substrate and become established, have formed in shallow 500 million years, but colonies can arise if conditions are suit- water. The Earth’s fi rst reef-building organisms corals similar to mod- able for growth. Given enough time, lived about 2.5 billion years ern colonial varieties coral colonies become thickets. As coral ago and were photosyn- have constructed reefs thickets build upward on the skeletal thesizing cyanobacteria that built stromatolites only during the past 60 remains of older colonies, a reef is estab- like these modern ones in million years. lished. Today, richly diverse coral reefs Shark Bay, Australia (top, are found in the tropics along coastlines, courtesy of the Australian Heritage Commission). What is a coral reef? on the margins of volcanic islands, and as Much of North America Corals are marine isolated coral . was once covered by tropi- animals related to jel- cal seas that were home to many species of coral. lyfi sh and anemones. Why are coral reefs in peril? Fossil corals, such as this Both colonial and Coral reefs can be damaged by natural one from (bot- solitary corals catch processes, such as storms, but they are tom), have been found in ancient reefs as much as plankton (microscopic increasingly at risk from human activities. 500 million years old, but plants and animals) and Coral reef health can be seriously affected modern colonial varieties other suspended food and the growth of new colonies hampered of coral have constructed reefs only during the past particles with arm-like by fi ne-grained sediment transported from 60 million years. tentacles, which feed a land into coastal waters as runoff. This sediment runoff can be greatly increased low-band disease are unknown. When Oil spills and pollutants can threaten entire by nearby land developments for agricul- corals are stressed, they often expel the reefs. Excessive nutrients from land sourc- ture, industry, and housing. Light neces- algal symbionts that are critical to their es, such as sewage outfall and agricultural sary for photosynthesis by symbiotic algae health in a process commonly known as fertilizers, promote the growth of algae living in corals is diminished in waters . One known cause of coral that can smother corals. Such algae also made cloudy or turbid by suspended sedi- bleaching is increases in ocean tempera- thrive when fish that graze on them are ment, reducing coral productivity. tures. Regional increases in sea-surface overharvested. Other organisms harmful Corals face serious risks from vari- temperatures occur during El Niño events, to corals, such as crown-of-thorns star- ous diseases, including black-band, and ocean temperatures worldwide may be fish, multiply when the species that prey white-band, and yellow-band diseases changing as a result of global warming. on them are removed. The collection of that have been reported from many lo- The susceptibility of corals to disease live corals and other reef organisms can calities worldwide. Black-band disease may be on the rise as a result of human ac- directly degrade large areas of reef. is primarily caused by cyanobacteria, but tivities. Many human activities are known the causes of white-band disease and yel- to directly and indirectly harm coral reefs.

CORAL REEFS DEVELOP IN CLEAR WARM SEAS . . .

Colonial “hard corals” form elaborate fi nger-shaped, branching, or mound-shaped structures and can create masses of limestone that stretch for tens or even hundreds of miles. Many coral reefs fringing coasts consist of nearshore inner reef fl ats that slope to deeper water fore reefs farther offshore. The reef crest, between the inner reef fl at and outer fore reef, lies in extremely shallow water and may be exposed during the lowest . Waves commonly crash against or break on the reef crest. Fringing reefs help to protect harbors, beaches, and shorelines from erosion and wave damage by storms. Volcanic Island

Shore Sea level

Inner reef (Reef flat)

Reef Reef crest limestone Outer reef (Fore reef)

Fringing reef

Coral atolls develop from reefs fringing volcanic islands (diagrams at right). As fi rst hy- Barrier reef pothesized by Charles Darwin, and confi rmed by ocean drilling done by British scientists a century ago, reefs fringing volcanic islands build vertically to sea level, forming steep- walled barrier reefs. As a volcanic island subsides, or sinks, with time, the growing reef keeps pace with the rising water lev- el. When the island eventually submerges, the ring-shaped reef forms an atoll with a central . The NASA Landsat 7 sat- ellite image at left shows Pacifi c islands with fringing reefs and an atoll. Atoll U.S. GEOLOGICAL SURVEY SEA-FLOOR MAPPING HELPS ASSESS REEF HEALTH

Fireworm The data used to cre- ate this 3-D perspec- tive image of West Flower Garden Bank, in the Gulf of Mexico, were collected and Threespot Damselfi sh processed by U.S. Loggerhead turtle Geological Survey scientists using multibeam sea-fl oor Blue Tangs mapping techniques.

Such techniques provide important information 94°20' W about a number of coral reef characteristics TEXAS that can be used to help evaluate and monitor Houston Brittle changes in reef health. The shallowest areas star shown in the image (red) reach to within 60 feet Galveston ico of the water’s surface and support a coral reef ex environment, home to a richly diverse web of f M f o 28°40' N ul life (see photos, copyrighted and courtesy of G David M. Read). STETSON EAST FLOWER BANK GARDEN BANK

0 40 MILES WEST FLOWER GARDEN BANK 0 40 KILOMETERS What is being done to protect coral reefs? Scientists worldwide are working to understand the impacts of natural pro- cesses and human activities on the health and sustainability of coral reefs. In the United States, this effort is being coordi- CORAL REEFS FACE MANY SERIOUS THREATS nated by the U.S. Coral Reef Task Force. Corals face serious risks from vari- Black-band disease, Florida ous diseases, including black-band As part of the task force, the U.S. Geo- disease. The susceptibility of corals logical Survey (USGS) is contributing to disease may be on the rise as to the effort to understand the biological a result of human activities. Many human activities are also known to and geological controls that affect our directly and indirectly harm coral Nation’s coral reefs. USGS coral reef reefs. Excessive nutrients from land research focuses on detailed mapping sources, such as sewage outfall and agricultural fertilizers, promote the of reefs, the development of monitoring growth of algae that can smother techniques, and studying reefs’ geologic corals. Such algae also thrive when growth and development and how they fi sh that graze on them are overhar- vested. Other organisms harmful are affected by sedimentary and hydro- to corals, such as crown-of-thorns logic processes, water quality, and fi sh- starfi sh, multiply when the species ing. These efforts will help provide in- that prey on them are removed. [Photographs courtesy of Florida formation that is essential if coral reefs Keys National Marine Sanctuary/ are to be saved. Exposed Page Gill (black-band disease); soil National Oceanic and Atmospheric Michael E. Field, Susan A. Cochran, and Administration (soil runoff, Hawai‘i); Kevin R. Evans and Fagatele Bay National Marine Edited by Sanctuary, /Kip Ev- James W. Hendley II and Peter H. Stauffer ans (crown-of-thorns starfi sh).] Graphic design by Crown-of-thorns starfi sh, Susan Mayfi eld and Sara Boore American Somoa Stream mouth For more information contact: U.S. Geological Survey Sediment plume Pacifi c Science Center 1156 High Street Santa Cruz, CA 95064 (831) 427–4745 http://coralreefs.wr.usgs.gov/ See also New Mapping Techniques Help Assess the Health of Hawai‘i’s Coral Reefs (USGS Fact Sheet 084–01). Soil runoff, Maui, Hawai‘i This Fact Sheet and any updates to it are available online at http://geopubs.wr.usgs.gov/fact-sheet/fs025-02/

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