They are colourful, have become a popular travel destination and are the home to a quarter of all marine life. Coral reefs inhabit and support the highest biodiversity of the world and whole marine food chains depend on them. Yet, they cover less than one percent – and decreasing – of the earth’s surface and are indispensable to 500 million people worldwide that depend on them for food, storm protection, jobs and recreation.
Why are coral reefs so important?
Coral reefs are often referred to as the rainforests of the sea. They are colonies for marine organism that secrete calcium carbonate over decades and centuries forming hard outer skeletal covers, the coral polyps. Corals can either reproduce sexually or asexually.
The most common reefs are barrier reefs, fringing reefs, patch reefs or atolls. Most of them occur in shallow water nearby the shore. Thus, they are especially vulnerable to human activities. Most ways humans exploit and harm the coral reefs are intrinsically woven into the social and economical way of living of coastal communities.
Threats to coral reefs
Some of these treats – naturally occurring but primarily man-made – are:
They are very sensitive to changes in light and temperature. Too warm see temperature – caused by global warming – corals expel the algae (zooxanthellae) living in their tissues. The algae provide up to 90 % of the coral’s energy. Expelling it, the algae turns white and starves to death. Some corals might look like rocks, but they are fragile. In 2016, a mass coral bleach killed between 29-50 % of the Great Barrier Reefs corals.
The most physical damage is caused by human activities. Coral reefs are destroyed by coastal developments, destructive fishing practices, boat anchors as well as recreational misuse (collecting corals for souvernirs, jewelry or aquarium decoration). A huge part of the pollution originates on the lands and finds it way into the coastal waters. Sedimentation from urban stormwater, forestry and agriculture run off smother corals interfere with their growth, feeding and reproduction.
Nutrients such as nitrogen and phosphorus from agricultural fertilizer use or pathogens from inadequately treated sewage and animal waste from livestock pens pollute the unique coastal ecosystems. Coral reefs are adapted to a low level of nutrients. The sudden excess can lead to an uncontrollable algae growth, which block the sunlight and consume oxygen that the coral would need for respiration. It can also support the growth of bacteria or fungi that can infect the corals with diseases. Fecal contamination can also cause diseases in corals through bacteria and parasites.
Sunscreen and microplastics
Even more harmful are the chemical substances that can be found in industrial and agricultural run offs. Metals, pesticides and organic chemicals can negatively affect the coral growth, reproduction and physiological processes. That includes sunscreen as well. Sunscreen was in fact invented in the American military. It all started in 1944, when US soldiers painfully realized how damaging the sun can and were looking for a suitable protection. It is important that we understand how our actions and for example sunscreen damages the remaining coral reefs.
Also trash plastic bags or discarded fish gear (marine debris) and microplastics snag on corals and block out the sunlight needed for photosynthesis. Microplastics can easily be consumed by fish and other sea life and kill the reef organism by poisoning them or starving them to death.
What happens when the coral reefs disappear?
At present rates scientist expect that by 2030 60 % of all remaining reefs are going to be highly or critically threatened. By 2050, only one quarter will be under medium threat with the remaining 75 percent at a high, very high, or critical threat levels. If we do not cool the oceans or can somehow restore our reefs, the world’s remaining corals will all be wiped out.
Worldwide people take efforts to save the reefs by setting up coral nurseries, identifying particularly resilient corals to heat and acidity and pioneering ways to quickly regrow them to repopulate reefs. Other scientist grow “super corals” to replant dying reefs but those corals are very sensitive and can oy grow under certain circumstances in warm and acidic waters.
Efforts are there but no widespread solution has been found yet. Looking at the predicted number: If we don’t deal with the problem soon, we should imagine how a widespread ocean ecosystem collapse looks like and what it means for us and the environment. Cities will lose their natural protection against storms and tsunamis; fishing and the tourism industry will suffer or maybe even be eliminated and whole marine food chains will collapse leading to the extinction of many species.