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Michael
E. Field, Susan A. Cochran, and Kevin R. Evans
US Geological Survey (USGS), October 2, 2002
US Coral Reefs - Imperiled National Treasures
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 of these complex marine ecosystems are poorly understood. Coral reefs are home to 25% of all marine species, and it is crucial that they be protected. Coral reef habitats contribute hundreds of millions of dollars annually to the United States fishing industry and help generate billions of dollars a year for the Nation’s tourist industry.
To preserve and protect the biodiversity, health, and social and economic value of coral reef ecosystems in the United States and its territories, the U.S. Coral Reef Task Force was established by Executive Order in 1998. The task force is a cooperative effort among Federal agencies, state agencies, and academic institutions and is co-chaired by the U.S. Secretaries of Interior and Commerce.
There are extensive coral reefs in the waters of the United States and its territories, covering more than 4 million acres of the sea fl oor in the Atlantic Ocean, Gulf of Mexico, Caribbean Sea, and the Pacifi c Ocean. More than 60% of the Nation’s coral reefs are found in the extended Hawaiian Island chain. Most of these are included in the recently designated Northwestern Hawaiian Islands Coral Reef Reserve, the largest U.S. nature preserve.
What is a reef?
The word “reef” has different meanings to different people. To a mariner, the term “reef” applies to shallowly submerged navigational hazards. To a surfer, a reef is an undersea obstruction that can make waves (and surfboards) break. Geologists and biologists generally restrict the defi nition of a reef to rigid biological constructions that have formed in shallow water. The Earth’s fi rst reefs were built by photosynthesizing cyanobacteria about 2.5 billion years ago. From fossil remains, it is known that a variety of organisms have constructed reefs, including bivalves (clams and oysters), bryozoans (coral-like animals), and sponges. Corals have been found in fossil reefs as old as 500 million years, but corals similar to modern colonial varieties have constructed reefs only during the past 60 million years.
What is a coral reef?
Corals are marine animals related to jellyfish and anemones. Both colonial and solitary corals catch plankton (microscopic plants and animals) and other suspended food particles with arm-like tentacles, which feed a centrally located mouth. Most hard corals also host symbiotic algae, a long-standing and successful partnership. These algae provide them with an additional food source through photosynthesis. Coral reefs are formed by corals that secrete hard calcareous (aragonite) exoskeletons, giving them structural rigidity. These colonial “hard corals” form elaborate fi nger-shaped, branching, or moundshaped structures and can create masses of limestone that stretch for tens or even hundreds of miles.
Although corals have a wide distribution in the world’s oceans, the varieties that form reefs are typically restricted to relatively shallow, warm tropical waters between latitudes 30° north and 30° south. Clean, clear water is essential to their health. Once coral larvae settle on a hard substrate and become established, colonies can arise if conditions are suitable for growth. Given enough time, coral colonies become thickets. As coral thickets build upward on the skeletal remains of older colonies, a reef is established. Today, richly diverse coral reefs are found in the tropics along coastlines, on the margins of volcanic islands, and as isolated coral atolls.
Why are coral reefs in peril?
Coral reefs can be damaged by natural processes, such as storms, but they are increasingly at risk from human activities. Coral reef health can be seriously affected and the growth of new colonies hampered by fi ne-grained sediment transported from land into coastal waters as runoff. This sediment runoff can be greatly increased by nearby land developments for agriculture, industry, and housing. Light necessary for photosynthesis by symbiotic algae living in corals is diminished in waters made cloudy or turbid by suspended sediment, reducing coral productivity.
Corals face serious risks from various diseases, including black-band, white-band, and yellow-band diseases that have been reported from many localities worldwide. Black-band disease is primarily caused by cyanobacteria, but the causes of white-band disease and yellow-band disease are unknown. When corals are stressed, they often expel the algal symbionts that are critical to their health in a process commonly known as coral bleaching. One known cause of coral bleaching is increases in ocean temperatures. Regional increases in sea-surface temperatures occur during El Niño events, and ocean temperatures worldwide may be changing as a result of global warming.
The susceptibility of corals to disease may be on the rise as a result of human activities. Many human activities are known to directly and indirectly harm coral reefs. Oil spills and pollutants can threaten entire reefs. Excessive nutrients from land sources, such as sewage outfall and agricultural fertilizers, promote the growth of algae that can smother corals. Such algae also thrive when fish that graze on them are overharvested. Other organisms harmful to corals, such as crown-of-thorns starfish, multiply when the species that prey on them are removed. The collection of live corals and other reef organisms can directly degrade large areas of reef.
What is being done to protect coral reefs?
Scientists worldwide are working to understand the impacts of natural processes and human activities on the health and sustainability of coral reefs. In the United States, this effort is being coordinated by the U.S. Coral Reef Task Force. As part of the task force, the U.S. Geological Survey (USGS) is contributing to the effort to understand the biological and geological controls that affect our Nation’s coral reefs. USGS coral reef research focuses on detailed mapping of reefs, the development of monitoring techniques, and studying reefs’ geologic growth and development and how they are affected by sedimentary and hydrologic processes, water quality, and fishing. These efforts will help provide information that is essential if coral reefs are to be saved.
This document is not necessarily endorsed by the Almanac of Policy Issues. It is being preserved in the Policy Archive for historic reasons.