Carbon pollution is warming our oceans and causing corals around the world to bleach. It has already led to increased levels of coral bleaching around the world, which are predicted to increase in frequency and severity in the coming decades. The mining and burning of coal releases carbon pollution into the air, which is heating our planet and warming our oceans.
If we continue to pollute the air and the ocean with carbon emissions at our high rate, coral reefs around the world will face a catastrophic future in coming decades — in our lifetime.
The stunning colours in corals come from a marine algae called zooxanthellae, which live inside their tissues. This algae provides the corals with an easy food supply thanks to photosynthesis, which gives the corals energy, allowing them to grow and reproduce. When corals get stressed, from things such as heat or pollution, they react by expelling this algae, leaving a ghostly, transparent skeleton behind. Some corals can feed themselves, but without the zooxanthellae most corals starve.
In some instances corals can recover from bleaching. If conditions return to normal, and stay that way corals can regain their algae, return to their bright colours and survive. However prolonged warmer temperatures and other stressors, like poor water quality, can leave the living coral in a weakened state. It can struggle to regrow, reproduce and resist disease — so is very vulnerable to coral diseases and mortality.
It can take decades for coral reefs to fully recover from a bleaching event, so it is vital that these events do not occur frequently. They serve as an early warning sign of what may happen to other less sensitive systems, such as river deltas, if climate change is not urgently addressed.
Once the tipping point for the survival of coral reefs is passed, the deterioration of other systems may cascade more quickly and irreversibly. If the agreement is fully implemented, we will likely see a decrease in atmospheric carbon concentrations. This will improve conditions for the survival of reefs, and enable other measures to rescue reefs to be successful.
Other measures alone, such as addressing local pollution and destructive fishing practices, cannot save coral reefs without stabilised greenhouse gas emissions. Reinforcing commitments to the Paris Agreement must be mirrored in all other global agreements such as the Sustainable Development Goals.
SDG 13, for instance, calls for urgent action to combat climate change and its impacts. There also needs to be a transformation of mainstream economic systems and a move towards circular economic practices. These are highlighted in SDG 8 inclusive and sustainable economic growth and SDG 12 sustainable consumption and production patterns.
Economic systems need to rapidly move to the low greenhouse gas emission scenario to enable global temperature decrease. A move away from current economic thinking should include the benefits provided by coral reefs, which are currently not taken into account in mainstream business and finance. Therefore, sustaining and restoring coral reefs should be treated as an asset, and long-term investments should be made for their preservation.
Investments should also include support for research at the frontiers of biology, such as genetic selection of heat-resistant corals that can withstand rising global temperatures.
Bleached staghorn with damselfish. Photo by Jodie Rummer. Zooxanthellae are tiny, colourful marine algae, which live inside corals, providing them with much of their colour and, most importantly, their primary supply of energy.
However, if the surrounding sea temperature becomes too warm, the algae die. Without zooxanthellae coral tissue becomes transparent, revealing the white coral skeleton beneath it. Once this happens, the corals can die if unfavourable conditions persist. If, however, temperatures return to normal levels, corals can regain their zooxanthellae, although the stress is likely to cause a decrease in growth and reproduction.
Future bleaching events are inevitable, but there are a number of important steps that we can take, locally, nationally and internationally to give the Great Barrier Reef a fighting chance. A concerted effort to reduce global carbon emissions will lessen the rise of ocean temperatures and ocean acidification. At the state level, we need to substantially improve the quality of water flowing on to the Reef.
Poor water quality is particularly harmful for coral growth, reproduction and the survival of young corals, severely limiting reef recovery potential. Furthermore, research shows that excessive nutrients arriving on the Great Barrier Reef trigger harmful crown-of-thorns outbreaks, which can devastate vast areas of the reef. How effectively we manage fishing, coastal development, pollution, trawling and shipping will play an important part in determining the future resilience of the Great Barrier Reef.
Take a look at our interactive map of the Great Barrier Reef. A healthy, resilient reef can either resist a stressful event, like bleaching, or recover from it. Corals can survive if water temperatures return to normal quickly. Home Ocean Facts What is coral bleaching? What is coral bleaching? When corals are stressed by changes in conditions such as temperature, light, or nutrients, they expel the symbiotic algae living in their tissues, causing them to turn completely white.
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