Both human and natural threats can cause deleterious effects on coral reef health. Hurricanes sweep across shallow water depths where corals live, creating swift currents and pounding waves that can overturn, rip up, and move around rather large corals. In recent years, El NiŅo has become a household term. El NiŅo's effects on corals are regional to global in scale. The primary result is higher than normal sea surface temperatures, causing symbiotic algae living in coral tissue to be expelled and making the coral appear to turn white. This outcome is called coral bleaching and can result in the death of the coral if the high water temperatures are consistent for a long period of time.

Human threats, which can be numerous, are displayed here. A recent study using fluorescent dyes has discovered that natural ground-water flow is in the direction from Florida Bay to the Atlantic Ocean. This direction indicates that if any pollutant enters the groundwater system on land, the possibility that it is transported toward the reef tract is great. The cause for ground-water flow was determined to be the result of tidal pumping: a phenomenon caused by the tidal fluctuation on the ocean side of the Florida Keys and the lack of tides on the bay side.

Natural Threats

HURRICANES ...

Spill-over of coral rubble after hurricane Georges	Fracturing of a spur formation at molasses reef after hurricane georges

(Click on map above for full-sized version.) Hurricane track lines from 1886-1992 that passed within 75 nautical miles of Miami, FL.

Removal of approximately 8 inches of sand from the base of this coral head after hurricane Georges	Elkhorn rubble at Grecean Rocks after hurricane Georges

	Entire elkhorn coral branches turned over after hurricane Georges, 1998 (left) and after hurricane Donna, 1960 (below).