National Oceanic and Atmospheric Administration 

U.S. Department of Commerce 

NOAA’s Oil Spill Response 

Oil Spills and Coral Reefs

Healthy coral reefs are among the most biologically 

diverse and economically valuable ecosystems on 

earth, providing valuable and vital ecosystem services. 

Coral ecosystems are a source of food for millions; 

protect coastlines from storms and erosion; provide 

habitat, spawning and nursery grounds for economically 

important fish species; provide jobs and income to local 

economies from fishing, recreation, and tourism; are a 

source of new medicines, and are hot spots of marine 

biodiversity. They also are of great cultural importance in 

many regions around the world, particularly Polynesia. 

Based on current estimates, 

shallow water coral reefs occupy 

approximately 284,300 square 

kilometers (110,000 square miles) 

of the sea floor. If all of the world's 

shallow water coral reefs were 

placed side-by-side, they would 

occupy an area a bit larger than the state of Texas. 

The total area of coral reefs represents less than 0.015 

percent of the ocean. Yet coral reefs harbor more than one 

quarter of the ocean’s biodiversity. No other ecosystem 

occupies such a limited area with more life forms. 

Reefs are often compared to rainforests, which are the 

only other ecosystem that can boast anywhere near the 

amount of biodiversity found on a reef. Coral reefs are 

sometimes called rainforests of the seas. 

Impacts of oil spills to coral reefs are difficult to 

predict because each spill presents a unique set of 

physical, chemical, and biological conditions. How corals 

are exposed to oil — and the composition of the oil at the 

time of impact — bears directly 

on how serious the impact will be. 

There are three primary 

modes of exposure for coral 

reefs in oil spills: 

4 Direct oil contact is possible 

when surface oil is deposited 

on intertidal corals that live 

near the surface of the water and become exposed 

with the tides. 

4 Rough seas and a light, soluble oil can combine to mix 

the oil into the water below the surface, where it can 

impact corals. Corals are exposed to less oil beneath 

the water surface, but the lighter oil components that 

mix easily are often the most toxic. 

4 Subsurface oiling can occur when heavy oils weather, 

or mix with sediment material. This increases the 

density of the oil to the point where it may actually 

sink, potentially smothering corals. 

Oil Spill Response Strategies for Coral Reefs 

Booms are sometimes used to control the movement 

of oil at the water surface. This should be done carefully 

in coral reef areas, as boom anchors can physically 

impact corals, especially when booms are moved around 

by waves. 

Dispersants act like detergents, breaking an oil slick 

into droplets that mix into the water column, where they 

dilute and eventually biodegrade. Dispersants work best 

on light oils, and are less effective on oil that has been 

(continued on back) 
extensively weathered or in areas of low water 

movement. Dispersants offer a trade-off of oil effects in 

the water versus at the shoreline. 

The use of dispersants over shallow submerged reefs 

is generally not recommended, but the potential impacts 

to the reef should be weighed against impacts that might 

occur to birds, mammals, turtles, and sensitive shoreline 

resources (such as mangroves) where it is extremely difficult to clean the oil. 

NOAA has produced two summary documents on corals 

and oil spills: 

A guide for planning and incident response - 

(http://response.restoration.noaa.gov/book_shelf/70_coral

_full_report.pdf) 

A synthesis of previous research on oil effects to corals ­

(http://response.restoration.noaa.gov/ book_shelf/1 

_coral_tox.pdf). 

In 2005, NOAA conducted an exercise to test 

emergency response to a simulated oil spill in the Florida 

Keys (http://sanctuaries.noaa.gov/safeseas/pdfs/safe 

seas2005.pdf). 

Effects of Oil and Dispersants on Coral Reefs 

Laboratory, field studies, and actual oil spill events 

often appear to show contradictory results for effects of 

oil and dispersants on coral reefs. 

The old notion that coral reefs do not suffer acute 

toxicity effect from oil floating over them is probably 

incorrect. Direct contact with spilled oil can lead to coral 

death, but depends on coral species, growth form, life 

stage, and type/duration of oil exposure. 

Longer exposure to lower levels of oil may kill 

corals, as well as shorter exposure to higher 

concentrations. Death may not be immediate, but 

rather take place long after the exposure has ended. 

Instead of acute mortality, it is more likely that oil 

effects occur in sublethal forms, such as reduced photosynthesis, growth, or reproduction. Early developmental 

forms (like coral larvae) are particularly sensitive to toxic 

effects, and oil slicks can significantly reduce larval 

development and viability. 

Coral communities may recover 

more rapidly from oil exposure 

alone than from mechanical 

damage. Recovery of coral reefs 

after oil exposure, however, may 

depend partly on the recovery of 

associated communities (e.g., nursery or foraging 

habitats, such as mangroves and seagrasses) that may be 

more seriously affected than the reef itself. Recovery time 

depends on the type and intensity of the disturbance and 

can range from several years to decades. 

Past Oil Spills Impacts to Coral Reef Ecosystems 

One extensively studied spill occurred at Bahia Las 

Minas, Panama in April, 1986. An estimated 60,000 ­

100,000 barrels of medium weight crude oil spilled into 

the waters of the bay, causing widespread lethal and 

sub-lethal effects to coral. 

In contrast, in the Arabian (Persian) Gulf Spill in 

January 1991, the largest oil spill in history, an estimated 

6.3 million barrels of oil were released. Given the 

magnitude of this release and the coral reef impacts noted 

at other tropical spills, there were dire expectations of 

severe impacts to reefs in Kuwait and Saudi Arabia. 

However, to date, the extent of coral reef damage directly 

attributable to the Gulf Spill has been remarkably minor. 

What You Can Do 

NOAA’s comprehensive efforts in response to the 

Deepwater Horizon event can be found at 

http://www.incidentnews.gov/incident/8220. 

Because oil is a hazardous material, volunteer 

opportunities are limited for unaffiliated, untrained 

volunteers. To report oiled shorelines or request volunteer 

information, please call 281-366-5511 or 866-448-5816. 

Learn more about NOAA’s response to the BP oil spill 

at http://response.restoration.noaa.gov/deepwaterhorizon. 

To learn more about NOAA, visit http://www.noaa.gov. 

May 12, 2010