What are the major threats to corals?

Factories and sewage treatment plants are two common sources of point source pollutants that can impact coral. View a larger image to learn more about this issue.

Many stressors to coral reefs originate from land-based sources, including dredging, coastal development, agriculture, deforestation, and sewage treatment. These activities often lead to sediments, excess fertilizer, toxic chemicals, as well as bacteria and viruses being transported to coral reefs by water running off the land, underground water seeping into coastal waters, and deposition from the air. Some pollutants, like excess fertilizer runoff from agricultural and suburban application, promote the rapid growth of algae that can take over areas where corals live. Other pollutants, like excess sediments, can smother corals directly.

Coral reefs are also affected by toxic chemicals, like leaking fuels and anti-fouling paints and coatings used on boats, bridges, etc. Petroleum spills do not always appear to affect corals directly because the oil usually stays near the water’s surface, and much of it evaporates within days. However, if an oil spill occurs while corals are spawning, the eggs and sperm can be damaged as they float near the surface before they fertilize and settle. These are just some of the ways toxic chemicals decrease the health of coral reefs, making them vulnerable to other threats like increasing ocean temperatures and disease.

Nonpoint source pollution can lead to corals being smothered by sediments, algal overgrowth, or being contamination by toxins. View a larger image and learn more about this issue.

As populations and development expand in coastal areas, land-based sources of pollution increase, threatening coral reef health. Learn more about this issue and download an infographic.