What are some of the threats to coral reefs around the world?
Increasing temperature.
With increasing ocean temperatures due to climate change, coral reefs are under threat. Coral reefs exist in a very specific temperture range. When the temperature they are exposed to is outside of this narrow range they become stressed. If they are exposed for an extended period of time the algae that produces nutrients for the corals to grow begin to die. The corals lose their colour – bleaching. Severe and prolonged bleaching can kill whole coral colonies, causing whole reefs to die.
Changing CO2 levels.
The ocean absorbs as much as 1/4 of the carbon dioxide produced each year from burning fossil fuels. With increasing levels of CO2 in the atmosphere the ocean is absorbing more and more. However the ocean is a very delicately balanced ecosystem. With increasing CO2 levels, the acidity of the ocean increases. This means animals such as corals, which make their exoskeleton using calcium carbonate, have to work harder and out more energy into maintaining these. The higher acidity is dissolving them, and reducing the amount of available salts for them to assimilate into their structure. This means less energy is assigned to growth and reproduction.
Multiple sources of pollution are threats to coral reefs.
Chemicals including metals, organic and man-made chemicals are threats to coral reefs. These chemicals which come from runoff from land, industrial discharges and mining activities. Even from something as simple as suncream, and other beauty products. Chemicals in cleaning products, as well as oil and fuel spills get into the ocean and stay there forever. Chemicals affect growth and reproduction in corals, as well as other physiological activities including feeding and defense responses. They affect the mutualistic relationship between the coral and the algae, resulting in bleaching and death.
Plastics and other man made items are threats to coral reefs, smothering them by preventing sunlight and oxygen from reaching the corals.
Excess nutrients can alter the pH of the environment, exacerbating the issue of increased CO2. They can also lead to the growth of algae which blocks sunlight, and consumes oxygen; cause harmful bacteria and fungi growth, which can be pathogenic to corals. Excess nutrients come from rainwater runoff from the land, including the excess use of fertilizers and from sewage discharge. Although disease in coral reefs can happen naturally, the presence of harmful substances including pathogens from wastewater can exacerbate the problem, not giving the corals a chance to heal
Physical damage.
Coral reefs act as coastal defense systems, taking a lot of energy out of storms as they approach land. The intensity and frequency of tropical storms is increasing. This causes extreme stress to coral reefs, often damaging them physically by breaking off sections of coral.
Coastal development including dredging and quarrying; destructive fishing practices including the use of explosives, or nets restricting the growth and smothering corals; deliberate destruction and harvesting of corals for the aquarium trade, jewellery and curios in the tourism industry; accidental damage from anchoring and grounding of boats; or from recreational misuse, for example touching and removing of coral, are all physically damaging reefs.
Overfishing changes the structure of the ecosystem. It alters the structure of the food web and causes cascading effects. For example removal of the grazing fish can mean the growth of algae gets out of control, smothering the coral.
