| Coral reefs exist in
the warm tropics at latitudes between 23.5N and 23.5S. Sometimes coral will
grow above or below these latitudes if there are warm currents such as the
Gulf Stream that pull warm water north or south from the tropics. At the
equator, the sun's rays are most direct and shine for a longer period of
the year than at other latitudes. The tropics, between the Tropic of Cancer
in the south and the Tropic of Capricorn in the north, are a range in which
the sun is directly overhead during a large part of the year keeping the
waters at a constant, warm temperature.
The closer to the surface of the water, the more sunlight the corals receive, which is essential for
photosynthesizing algae. Yet the coral cannot live above water for long. The depth at which coral can exist also depends on the cloudiness of the water. The waters in the Caribbean tend to be clear because there are not a lot of dissolved nutrients
floating in the currents promoting plankton growth. In other parts of the world the water is not as clear due to high plankton activity, therefore the sun's rays do not penetrate as deeply.
Large amounts of nutrients such as nitrogen and
phosphorous, brought in by the ocean waves are essential for the growth of coral. However, even though there are a lot of nutrients flowing out of the mouths of rivers, corals do not grow in these areas because the water is clouded with mud or silt.
Corals also cannot survive near or in freshwater sources, such as a river or a lake.
Sarah H. Dawson
NOAA Paleoclimatology Program
Click on above image to enlarge.
Download a zip file
of a full resolution TIF image