The impact of climate change and plastic pollution on the world’s corals

In conjunction with World Oceans Day and International Year of the Reef, Ian Chai from our conservation team shares some facts about corals and why the world’s coral reefs are under serious threat.

Corals are found in tropical seas where temperatures are well regulated. They typically thrive in warmer waters between 23 and 29 degrees Celsius and can be pretty sensitive to fluctuations in water temperatures, especially when they hit the extremes.

Most corals require sunlight to survive. This is why they are usually found in shallower depths where sunlight is able to reach them.

Birds Nest Coral
Birds Nest Corals are one of the fastest growing hard corals. Image credit: Boon Ping, aquarist at S.E.A. Aquarium

An integral part of the marine ecosystem

Coral reefs are hosts to a wide range of marine life and act as a natural ‘breakwater’ for coastal habitats and settlements, thus preventing coastal corrosion.

Interestingly, they are also the ocean’s natural filtration systems. Being filter feeders, corals consume particulate matter suspended in the water column, helping to maintain the quality and clarity of shore waters.

Extreme close-up of the Rumphella Coral. This coral uses its fuzzy tentacles to capture planktonic organisms and microscopic food particles from the water column. Image credit: Boon Ping

The impact of plastic pollution on corals

Plastic debris do not just end up being mistakenly eaten by marine animals. These bacteria-ridden debris often have sharp edges that may cut open the coral’s delicate skin, exposing them to bacterial infection.

Bigger pieces of plastic trash may also block out sunlight. This prevents the zooxanthellae (symbiotic algae living within the corals) from providing oxygen to the corals through photosynthesis. At the same time, it creates conditions for certain pathogens to thrive.

Scleractinian coral (hard corals) have been known to ingest microplastics. Though the implications of this discovery has yet to be understood in relation to corals, microplastics have been known to have adverse impact on marine animals, which means corals may be similarly affected.

Brain Coral
Close-up of the brain coral, a common type of hard coral. Image credit: Boon Ping

How climate change affects corals

Zooxanthellae are tiny, colourful marine algae that live inside corals, providing them with colour and food. Bleaching (corals turning white or very pale) is the result of this symbiotic algae being expelled due to stressors like pollution, excessive sunlight or unusually high water temperatures.

In recent years the frequency and widespread occurrence of coral bleaching has increased exponentially, and mass coral bleaching events has plagued marine habitats worldwide. This is largely attributed to the increase in water temperatures around the world due to global warming.

Image source: International Year of the Reef

As ocean temperatures increase, the photosynthetic reaction of zooxanthellae is greatly compromised, reducing their ability to produce sugars and causing a buildup of toxic by-products. In order to save itself, the coral would expel the zooxanthellae and some of its tissues from its body, a process called tissue sloughing. This process results in the bleaching of corals.

Bleached corals without zooxanthellae will slowly starve to death. However, when temperature returns to the right level, zooxanthellae is able to recolonise the corals, thereby allowing the corals to regrow.

To do my part for the ocean, I will be participating in a reef cleanup on 9 June 2018. Organised by Guardians of the S.E.A.A., this cleanup will see about two dozen divers clean up two dive sites around Pulau Hantu.

If you wish to learn more about marine conservation and take part in meaningful activities like beach cleanups and reef cleanups, join us as Guardians of the S.E.A.A..

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