Global Decline of Coral Reefs
It takes a long time to build a coral reef. The animals that create coral reefs have evolved over millions of years, continuing to slowly deposit the calcium carbonate that forms their characteristic ocean homes. Bathed in warm tropical waters, the coral animals and their symbiotic algal partners evolved to survive at the upper limit of ocean water temperature.
Together, climate change and human activity pose dual threats to the long-term survival of the world’s coral reefs. As global warming due to fossil fuel emissions raises ocean temperatures, coral reefs are suffering. The excessive warmth causes the reefs to expel their symbiotic, food-producing algae, resulting in a phenomenon known as bleaching. When bleaching occurs, the reefs lose much of their characteristic color as the algae and the coral animals die if loss of the symbiotic zooxanthellae is prolonged.
Rising levels of atmospheric carbon dioxide further threaten the corals in other ways; as CO2 dissolves in ocean waters, it lowers the pH and increases ocean acidity. As acidity increases, it interferes with the calcification that normally occurs as coral animals build their calcium carbonate homes.
When a coral reef begins to die, species diversity plummets as animals lose food and shelter. Coral reefs are also economically important tourist destinations, so the decline of coral reefs poses a serious threat to coastal economies.
Human population growth has damaged corals in other ways, too. As human coastal populations increase, the runoff of sediment and agricultural chemicals has increased, too, causing some of the once-clear tropical waters to become cloudy. At the same time, overfishing of popular fish species has allowed the predator species that eat corals to go unchecked.
Although a rise in global temperatures of 1–2˚C (a conservative scientific projection) in the coming decades may not seem large, it is very significant to this biome. When change occurs rapidly, species can become extinct before evolution leads to new adaptations. Many scientists believe that global warming, with its rapid (in terms of evolutionary time) and inexorable increases in temperature, is tipping the balance beyond the point at which many of the world’s coral reefs can recover.
What are the effects of global climate change and increasing levels of carbon dioxide on the coral reefs? How does it affect the local ecosystem?
- Due to rising temperature, coral reefs lose their symbiotic partner, the algae, in the process called bleaching. Rising CO2 changes the pH of water, which interferes with calcification. Animals whose source of food is coral reefs also decline in numbers.
- Due to rising temperature the hard calcium carbonate skeleton of coral reefs is destroyed due to a process called bleaching. Rising CO2 changes pH of water which interferes with calcification. Animals whose source of food is coral reefs also decline in numbers.
- Due to rising temperature, coral reefs lose their symbiotic partner, the algae, in the process called ocean acidification. Rising CO2 changes the pH of water, which interferes with calcification. Animals whose source of food is coral reefs also decline in numbers.
- Due to rising temperature, coral reefs lose their symbiotic partner, the algae. Rising CO2 changes the pH of water through the process called bleaching. Animals whose source of food is coral reefs also decline in numbers.