Impacts to Coral Reefs

Human impacts on coral include:        
  • Pollution       
  • Overfishing        
  • Tourism
  • Aquarium/Souvenir Trade        
  • Global Climate Change

Coral reefs are threated by human activities throughout the world. In southeast Asia, the hot spot of coral
diversity, more than 80% of the reefs are at risk from coastal development and harmful fishing practices.

                                                                Macro algae


Population growth and development threaten the survival of coral reefs
Population growth and urban development currently rank among the greatest threats to coral reefs.
Development activities cause erosion, resulting in the run-off of sediments which eventually reaching the
reefs. Also storm water runoff carries fertilizers and sewage into the ocean, damaging coral reefs. Increase
of nutrient concentrations within the reef environment is followed by increase of algae, which may smother
corals. Whether it is from direct sedimentation or an increase in turbidity from nutrient-loading, the amount
of sunlight reaching the corals is reduced.

                                                      Shrimp boats


Over fishing has altered ecological dynamics of marine communities
Along with human population growth, the harvest of resources from the sea is ever-increasing. Overfishing
has changed the ecological dynamics of marine communities, allowing some organisms to dominate
reefs that once were kept in check by large reef fish populations. Fishing practices have also become more
destructive as fish populations decrease. In some regions, indiscriminate fish traps are used while in other
areas the use of dynamite and cyanide have become common practice.


Increase in tourism is responsible for increase in reef damage.
Coral reefs attract ecotourists, bringing much needed currency to tropical regions. Ironically, the increase in
ecotourism is usually accompanied by an increase in reef damage. Divers and snorkelers may harm the
corals by touching the polyps, while the boats transporting ecotourists to the reef may damage the reef by
dragging anchors. Although ecotourism is responsible for reef damage, if it is carefully managed and
monitored, ecotourism may actually help preserve these valuable habitats.

Aquarium and Souvenir Trade    

Fish and invertebrates are harvested from the world's coral reefs.
Many species of fish and invertebrates are harvested from the world's coral reefs for the aquarium industry.
Unfortunately, poisons such as cyanide are often used in the Indo-Pacific region, causing the deaths of
many fish and surrounding corals. After the live fish are collected, up to half die as a result of poisoning or
stress. Those that do survive have high mortality rates in home aquariams due to dietary and physical
requirements. Corals and shells are also collected throughout the world and sold as souvenirs to tourists,
made into jewelry, or exported as curios.

                              Climate Change Research - Data Collection

Global Climate Change   

Rising sea temperatures cause coral bleaching
Global climate change may cause increases in sea temperature and sea level as well as ocean current
patterns, all of which can cause damage to reefs. Corals are very sensitive to water temperature changes,
with rises in temperature resulting in coral bleaching episodes.
Natural impacts on corals include:    
  • Storms         
  • Thermal Stress     
  • Diseases

Storms and hurricanes may cause extensive damage to reef structures and communities.  Although much
of coral reef destruction is blamed on human activity, natural disturbances are also capable of causing
extensive damage to coral reefs. Strong waves caused by storms and hurricanes may smash into the reef,
breaking up large corals and creating rubble fields. Storms also harm reefs indirectly by disrupting near
shore habitats, resulting in the release of large amounts of sediments and freshwater to come into contact
with the reef. These disturbances open spaces for new organisms to colonize, preserving overall

Thermal Stress
Thermal stress can induce the loss of symbiotic algae from corals, often referred to as "coral bleaching".  
Heat-related stress often occurs during late summer months when the sun is intense. Corals can survive
water temperatures as high as 86-95°F (30-35°C), depending upon the species. Increases in water
temperature often causes loss of symbiotic algae from coral tissues, referred to as coral bleaching.
Corals are also susceptible to cold stress at temperatures at or below 57°F (14°C). Cold water masses
originate in Florida Bay, causing coral death in patch reefs long the water current's path. However, most
offshore corals experience little damage due to the mixing of the cold water current with the warm offshore
waters, moderating temperatures and lessening the impact on surrounding reefs.


Coral reef organisms, such as the long-spined sea urchin, are susceptible to many pathogens.  Along
with coral bleaching, black band disease, and white band disease, coral reef organisms are subject to
many pathogens. During the 1980s, a water-borne pathogen caused the massive die off of the long-
spined sea urchin, Diadema antillarum. Long-spined sea urchin populations were reduced as much as
95% in some locations. This urchin is an important herbivore, keeping algae growth in control in reef
habitats. The decline in sea urchin populations resulted in algal overgrowth throughout the reefs of the
Natural Threats to  Coral Reefs
Florida Keys National Marine Sanctuary