Why are coral reefs in peril and what is being done to protect them?

Coral reefs can be damaged by natural processes, such as storms, but they are increasingly at risk from human activities. Oil spills and pollutants can threaten entire reefs. Excessive nutrients from land sources, such as sewage and agricultural fertilizers, promote the growth of algae that can smother corals. Other organisms harmful to corals, such as crown-of-thorns starfish, multiply when the species that prey on them are removed.

Coral productivity is also decreased when land developments for agriculture, industry, and housing increase sediment transported from land into coastal waters as runoff. This clouds the waters and blocks light necessary for photosynthesis by algae living in corals. Corals face serious risks from various diseases. 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, possibly due to global warming.

Scientists worldwide are working to understand the impacts of natural processes and human activities on the health and sustainability of coral reefs. The 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, studying reefs' geologic growth and development, and how they are affected by water quality, fishing, and sedimentary and hydrologic processes. These efforts will help provide information that is essential if coral reefs are to be saved.

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Image: Coral Reef Affected by White Syndrome
January 6, 2012

Coral Reef Affected by White Syndrome

Coral reef affected by Montipora White Syndrome. Note the large swath of white skeleton tissue surrounded by normal (brown) corals.

Attribution: Natural Hazards
December 17, 2010

Corals: A 50-Year Photographic Record of Changes

This video podcast highlights 50 years of photographic documentation of coral reefs in the Florida Keys.  The photographs show 5 decades of changes that have taken place in both the size and the types of corals that were present at several coral reef sites from the early 1960s to today.  The images capture events such as the appearance of coral disease and the die off of

January 29, 2010

PubTalk 1/2010 — Coral Reefs, the 6th Extinction, and You

By Michael Field, Senior Marine Geologist


  • Five major episodes of biological extinction have occurred on Earth during geologic time -- what caused these extinctions and why are they relevant today?
  • Scientists are concerned that life on Earth may be facing a 6th major extinction, severely limiting the biodiversity of animals and
Image: Black Band Disease on Great Star Coral
August 3, 2009

Black Band Disease on Great Star Coral

Black band disease on Great star coral, Montastraea cavernosa. The white areas are exposed coral skeleton, the black band is the active disease zone, and the brown polyps are living coral.

Attribution: Ecosystems
Image: USGS Coral Reef Researcher
July 9, 2009

USGS Coral Reef Researcher

Don Hickey finishes installing ocean chemistry monitoring equipment on Sombrero Reef, Florida Keys.

Attribution: Water Resources
April 14, 2009

Coral Concern: The World's Reefs Face Big Issues

Coral reefs are one of Earth's most beautiful and vital ecosystems—and they are declining at a rapid pace.

Mike Field, Chief of the USGS Pacific Coral Reef Project, talks about the importance of coral reefs and how pollution, climate change, and other factors are affecting them.

July 17, 2008

What is a reef?

Listen to hear the answer.

video thumbnail: Coral Sampling
July 30, 2004

Coral Sampling

Small sprigs of glass coral are snipped off by the submersible's manipulator and transferred to a multi-chambered sampler for bacterial and genetic analyses. Attracted by the disturbance, a large Conger Eel (Conger oceanicus) then a Snowy Grouper (Epinephelus niveatus), investigates the scene.

Fish swim around a brightly colored coral reef
November 30, 2000

Coral Reef