Threats to Coral Reefs

Corals and coral reefs are extremely sensitive. Slight changes in the reef

environment may have detrimental effects on the health of entire coral colonies.

These changes may be due to a variety of factors, but they generally fall within two

categories: natural disturbances and anthropogenic disturbances. Although

natural disturbances may cause severe changes in coral communities,

anthropogenic disturbances have been linked to the vast majority of decreases in

coral cover and general colony health when coral reefs and humans occur

together. One of the greatest threats to coral reefs is human expansion and

development. As development continues to alter the landscape, the amount of

freshwater runoff increases. This terrigenous runoff may carry large amounts of

sediment from land-clearing areas, high levels of nutrients from agricultural

areas or septic systems, as well as many pollutants such as petroleum products or

insecticides. Whether it is direct sedimentation onto the reef or an increase in the

turbidity of the water due to eutrophication, decreases in the amounts of light

reaching corals and may cause bleaching.

In addition, increases in the amounts of nutrients enhance the growth of other

reef organisms such as sponges which may outcompete the corals for space on

crowded reefs.