Coral Reefs - All You Need to Know

Sailing - maybe snorkelling or diving? SW

A wondrous world below © SW

Why Are Coral Reefs Important?

Corals on a reef act much like trees in the forest: they provide both the physical structure and life supporting ‘powerhouse’ which supports a range of habitats (homes) for plants and animals.

Different habitats, separated by variations in light (affected by both depth and shading), nutrient levels, temperatures, water movements created by waves or currents, and depths, create so many different habitats that coral reefs can lay claim to among the highest numbers of species co-existing in one area on the planet. The scientific term for this great richness of life is ‘biodiversity’ and coral reefs are important partially because of their high biodiversity.


Coral reefs occur in warm, relatively shallow tropical seas. Their great abundance of life seems almost out of place in these clear, comparatively barren tropical seas – sometimes referred to as ‘tropical deserts’ because they are so low in nutrients. But what the oceanic water lacks, the reefs make up for. A unique partnership exists between corals and the microscopic single-celled algae which live inside them. This symbiotic relationship is the basis for the complex, interconnected web of life that we call ‘coral reefs’.

The colour tells the story © SW

In these days of deep concern about climate change and control of carbon in our atmosphere, it is also worth remembering that coral reefs, like rain forests, play a very significant role as ‘carbon sinks’. They do this by locking dissolved carbon dioxide into the calcium carbonate that forms their skeletons.

Coral reefs also play vital roles for the people who live along their nearby shores. They act as buffers, protecting coastlines from erosion caused by strong wave action during storms. They are also a major source of food – one estimate reveals that coral reefs provide food for one billion people in Asia alone. The larger coral reef systems may produce enough seafood to support both local consumption and a thriving export trade.

Indeed, the economic value of coral reefs often plays a key role in local economies. In addition to fish and other sea food, they are a source of medicinal products and very often of thriving tourism generated by visiting divers, snorkelers, recreational fishers, sailors and other holiday makers.


Current Threats to Coral Reefs

Coral reefs are in danger almost everywhere, whether as a result of local conditions or from global changes, or both.

This is a very serious situation for our planet. A quarter of the planet’s existing coral reefs are recognised as biodiversity hot spots, places that support unusually high numbers of different species and are at serious risk of being lost forever.

So what’s killing them?
The answer, unfortunately, is a large number of different human activities and related global conditions.

Let’s start with land-based activities. Unfortunately people are slow to realise the impact these can have on coastal marine life. Pollution in the form of silt, fertilizers, sewage, agricultural and industrial run-off is flushed down streams and rivers into the ocean. The culprit projects, such as forestry or mining, are frequently many kilometres inland.

Fish need the coral © SW

Their transported wastes damage water conditions around the reefs themselves. Silt, for example, reduces light intensity and clogs delicate coral polyps. Sewage and fertilizers unnaturally boost nutrient levels causing an algae bloom, called eutrophication, which starves reef life of light and oxygen.

This can also be caused by yachts dumping their sewage on sheltered reefs where water exchange with the open ocean is restricted.

Unfortunately coral reefs, by their very nature, attract many of the activities
that are causing their downfall. Local abundance of fish creates the illusion that such stocks are inexhaustible. Nothing could be further from the truth and destructive fishing practices such as – almost universal over-fishing, dynamite fishing (the impact bursts the swim bladders of reef fish, causing them to float to the surface) and poison fishing (the use of cyanide to stun and capture live reef fish) have devastating effects on reef life.

Commercial fishing operations among coral reefs usually target particular species of fish. For example, herbivorous (plant-eating) fish are sought-after as aquarium pets and their removal from a reef breaks a previously connected ‘food chain’. Without these fish to keep it well grazed, algae can grow unchecked, overtaking the corals and other fixed reef inhabitants such as sponges, sea-fans and tubeworms.

Tourism can add more pressure to the reef, but it is sometimes possible
to control. Sailboat anchoring over corals and dumping of rubbish and sewage also cause problems for the reefs and their associated marine life.

Plastic bags are enemies to fish, dolphins, turtles and the corals themselves! Often the most well-meaning of visitors to coral reefs are a source of damage. Divers, snorkelers and reef walkers routinely break corals merely by touching them, a trauma that may result in the whole colony dying.

Snorkelling or diving the experience is inspiring © SW

Natural Events such as hurricanes and cyclones can devastate reefs,
breaking pieces of coral that have taken hundreds of years to develop. An increase in El Niño related storms in recent years has been linked to ncreased reef damage. These events also cause coral bleaching.

Corals are animals made up of two parts, a hard skeleton and the soft polyp
within. Inside each of these polyps live symbiotic algae, single-celled plants using sunlight to create oxygen and nutrients which are exchanged with the coral polyps for carbon dioxide and other requirements.

Certain conditions can trigger an en mass exodus of the symbiotic algae from the coral which leave it white and dying. This is what is meant by coral bleaching and the good news is that it can be reversible, with the symbiotic algae returning to the coral before it dies.

There are also times when one reef member causes havoc for the rest of the reef. ‘Plagues’ of Crown of Thorns Starfish have devastated large areas of coral reefs. These animals eat their way through many kilometres of reef and produce thousands of larvae which settle on nearby reefs and continue the destruction. The doubt is whether the sudden population explosions are triggered by natural causes, by human kind, or both! The response is often to gather divers together and physically remove the adult starfish from a reef area.

When an outbreak was discovered in Bunaken Marine Protected Area
(Pasir Panjang) in 2003, local managers, fishermen, divers and others began removing them from the reef hopefully prior to their spawning. Within a year, at least 2300