Coral is very seriously endangered by humans. This includes silting up the reefs, coral extraction, nutrient pollution, industrial pollution, rubbish that we dump in the oceans and even radioactive waste. Find out more about it below!
Silting of coral reefs
Corals are naturally resistant to small amounts of silt. This is necessary because they are always exposed to sand that is carried away by the current and waves or that is swirled from the bottom. Coral colonies are washed clean from time to time by tides and currents. Some species help with this by moving their polyps and tentacles in such a way that it rinses clean faster. However, most corals are sensitive to high or increased silt concentrations and are quickly affected or eventually die.
Large amounts of sediment suffocate the coral. The polyps no longer receive oxygen and important nutrients. Due to these large quantities, there is no longer enough sunlight on the zooxanthellae and that hinders photosynthesis, which in turn means part of the nutrition for coral. The sediment is also bad for the animals on the reef, because they use the coral as a shelter. When the coral has silted up, the hollows where they used to hide have become inaccessible. Much of the heavy sediment that ends up on the reefs comes from land. Any soil that is not retained by a plant cover is exposed to erosion. There are numerous causes of erosion such as mining, construction work and all kinds of mining projects.
Today, road construction is a major culprit. Country roads are being built, but these are made of sand or something similar. During a real rain shower all this sand washes into the sea and that way a lot of sediment ends up in the water. However, it does not all have to take place close to the sea, for example the burning of forests. That way, much less of the bottom is retained and a lot of soil washes down, eventually ending up in the seas.
Mangrove forests are very beneficial in terms of sludge absorption. They naturally catch part of the washed away soil, but this is getting less and less. More and more mangrove forests are being removed by human action.
Also due to dredging, a lot of sludge ends up in the water. This can end well for the coral, but it can also have disastrous consequences. If there are a lot of massive corals, it will not have much effect, because they require little living food. However, it is the more vulnerable species that have to do with the sludge, there is a major problem. Very large parts of the reef will then die.
Coral extraction
A lot of coral is extracted for construction projects. Coral is often much cheaper than rocks, for example. This coral extraction mainly takes place on islands. The coral is often taken from the reefs close to the coast. The residents justify the extraction by saying that the coral will grow again. This is of course the case, but the extent to which the coral is now being extracted is so great that the coral can no longer keep up.
Nutrient pollution
The tropical waters that contain reefs are usually poor in nutrients such as nitrates and phosphates. Fertilizer and sewage water, which is rich in nitrates and phosphates, is discharged into the water. This is an enrichment of the water with mineral and organic nutrients, but there is also a disadvantage. As with all of the foregoing, it shouldn’t be too much. If it is present in excess, the reef animals die from lack of oxygen. Seaweeds benefit from this nutrient richness, but it means destruction for the coral. High nitrate concentrations are toxic to corals and phosphates stunt skeletal growth. When there are so many nutrients, the seaweeds will dominate the reef. That way, less sunlight can reach the coral and at some point the reef will be completely blurred. The phytoplankton in the upper layers of the sea benefits from these nutrients and their density increases. This means that even less light reaches the coral. Herbivorous fish and echinoids can keep the seaweed in check for a long time, but at some point this will stop. This may be due to overfishing, but also due to a natural decline in the sea urchin population.
In the open sea, where there are strong currents, the sewage water is not a big problem. In fact, it may be beneficial, as certain species of fish visit these places to look for their food. However, if the sewage is discharged into nearby lagoons, it can have disastrous consequences. The lagoons have standing water and in this way the water stays in contact with the reef for a longer period of time. It is also bad for humans, because there is a risk of jaundice, cholera and typhoid at the end sewer. These diseases are transmitted by filterers such as mussels and oysters, which absorb the sewage water.
Industrial pollution
Little is known about chemicals and metals and the damage to the coral. Research shows that there are large differences per area. The chlorine compounds are known to affect reef animals, particularly the larvae in plankton. Many pesticides are poisonous and increase the effects of the washed away fertilizers: not just sludge, but poisonous sludge is formed.
Power plants are still discharging warm water into rivers or directly into the sea, which can increase the water temperature, which is a major problem for the reefs.
Then you also have oil pollution. This is not only caused by oil tankers crashing, but also leaking pipelines and cleaning the oil tankers are culprits. The oil has caused virtually no short-term problems for the coral itself, but it has caused the animals that live there. Fish that are completely covered in oil, but also birds that suffer from it.
Human clutter
Every year a lot of rubbish is discharged into the sea, a large part of which is almost impossible to break down plastic, but also nylon fishing lines. This is deadly to many animals. Think of fish, birds and turtles that get caught in the nylon fishing lines and choke. Or animals that choke after eating plastic bags, balloons or other objects that look like jellyfish.
A small amount of debris can be harmful to a reef, not just the animals. The coral can be completely buried under the plastic and catch little or no sunlight. In this way, it can also have negative consequences for coral.
Radioactive pollution
Reefs have suffered from three types of nuclear testing: above ground, undersea and underground. Underwater explosions had the greatest impact on reefs, hitting craters in which life had been destroyed and throwing a “soup”. of sand and coral on those nearby corals and choked all other filterers. Even in the event of an explosion in deep water, well below the level where corals grow, the subsequent shocks can knock over immense chunks and drop down the reef.
In atmospheric nuclear tests, the polyps scorch, skeletons melt into lime, burn fish in shallow lagoons, and shock waves roll through the water, breaking off delicate corals and throwing them upside down. In all explosions, fish are killed by shock waves bursting their swim bladders, kidneys and liver or causing bleeding. They also often die in collapsing caves or under falling pieces of coral. Aboveground and submarine nuclear tests have now stopped, but French Polynesia is still working on underground nuclear tests.
The radioactivity from these nuclear tests first contaminates the phytoplankton and seaweed and is then passed on in ever-increasing amounts via the food web to invertebrates, fish and finally to humans. The radioactivity has a direct effect on the coral. Coral can reproduce less well or even not at all and it can break down during the tests.