| Humans are increasingly causing damage to coral reef | | | | eventually empty into the sea. Similar effects may be |
| ecosystems by creating widespread environmental | | | | produced by activities associated with the |
| alterations of a kind seldom sustained or encountered | | | | development or urbanization of coastal areas. This |
| over such large areas through the long evolutionary | | | | often involves dredging boat channels, building |
| history of coral reefs. For such environmental | | | | marinas and coastal resorts, and the deposition |
| changes, coral reef communities have evolved no | | | | (dumping) of materials from construction sites directly |
| long-term defenses. | | | | into the sea. |
| Here, we discuss the three greatest threats currently | | | | Such land-based activities have the capacity to |
| posed by human activities that could, with proper | | | | quickly devastate coral reef ecosystems unless |
| regulation, be quickly controlled. The fourth major | | | | properly engineered and controlled. Waters clouded |
| threat, current global warming, is a long-term problem | | | | with silt are not conducive to reef growth or survival. |
| with no short-term solution. | | | | Corals vary in their ability to rid themselves of |
| 1. Nutrient Overload (Eutrophication). Under natural | | | | sediments - some are able to deal with limited |
| conditions, tropical seas contain inherently low levels | | | | amounts quite well, but many are not. |
| of dissolved nutrients (nitrates and/or phosphates). | | | | Sediments cloud the water, reducing sunlight available |
| This fact, combined with the grazing of coral reef | | | | for photosynthesis, smothering live corals, and |
| herbivores, acts to keep macroalgal growth on hard | | | | reducing the ability of coral reef fishes to see and |
| coral surfaces to a minimum. But when the waters | | | | capture prey. The removal of coastal mangroves and |
| around coral reefs become abnormally enriched with | | | | seagrass meadows - which are highly efficient natural |
| nutrients, macroalgal growth exceeds the capacity of | | | | sediment "traps" - exacerbates this problem by |
| reef herbivores to keep plant growth in check. | | | | allowing increased amounts of terrestrial sediments to |
| Macroalgae then gains the upper hand, and the reef | | | | disperse in coastal seas. Turbid water also inhibits or |
| substrate "shifts" from one dominated by live coral to | | | | prevents photosynthesis. |
| one instead largely covered by seaweeds. | | | | 3. Overfishing. Overfishing refers to the continued |
| Therefore, a form of pollution particularly destructive | | | | harvest of populations unable to sustain the level of |
| of coral reefs is the discharge of otherwise | | | | fishing/collecting pressure applied, resulting in |
| "seaweed limiting" nutrients into coastal marine | | | | continued population decline. For coral reef |
| environments. Sewage, storm water runoff, fertilizers | | | | ecosystems, overfishing along with the use of |
| and other forms of nutrient-loaded discharges from | | | | habitat-destructive fishing/collecting has decimated |
| homes, factories and farmlands far inland are often | | | | coral reefs and associated marine life in coral reef |
| carried directly to coastal seas by rivers and canals, | | | | areas throughout much of the world. |
| or percolate down through porous soils into the | | | | The use of chemical poisons, including bleach, soaps, |
| underlying aquifer and subsequently travel for many | | | | and even cyanide to drive marine life from the reef |
| miles to eventually emerge in coastal waters and | | | | or to incapacitate fishes for capture is common |
| coral reef areas. | | | | practice today in many reef areas, despite prohibitive |
| Recent research has indicated that coral reefs have a | | | | legislation. Even worse, explosives are commonly |
| very low tolerance for this form of pollution; a | | | | used in some areas to stun and kill fish. These |
| seemingly very small increase in the amounts of | | | | shatter the reef structure, destroying in an instant |
| dissolved nutrients present may lead to wholesale | | | | that which took thousands of years to create. |
| changes in reef substrates. This has probably been a | | | | Fish trapping for local markets, the collecting of corals |
| major cause of reef damage in many coastal areas, | | | | and shells for souvenirs, jewelry and trinkets, and the |
| including the shallow seas that bathe the only living | | | | collection of juvenile reef fish for the aquarium trade |
| coral reefs to be found in the continental United | | | | are all serious and increasing problems for the health |
| States - those of the Florida Keys. | | | | of coral reef environments and communities. The |
| 2. Sedimentation. When upland or coastal forests and | | | | removal by any means of excessive numbers of |
| savannas are stripped of natural vegetation through | | | | animals from reef areas may have lasting deleterious |
| clearing and burning, there is little left to trap or hold | | | | effects on many aspects of reef community ecology |
| soils in place. Rains then carry far greater loads of | | | | changes and effects poorly understood at present. |
| sediments directly into streams and rivers that | | | | |