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Illustration of Coral Bleaching
Illustration of Coral Bleaching. (Source: theguardian.com)

About 18% of the world’s coral reefs grow in Indonesia, with an area of ​​50,785 square kilometers. Coral reefs provide shelter for fish, protect coastal areas from erosion and storms, and provide livelihoods for fishermen and tourism industry workers. So many benefits of coral reefs in our seas, and yet, there is one threat to the existence of coral reefs, namely coral bleaching.

Getting to Know Coral Bleaching

Coral reefs consist of many polyps, a small sac-shaped animal that has a blooming tip with small tentacles. In the polyps, there are small algae called zooxanthellae. These tiny algae are what give coral reefs their color.

The relationship between coral reefs and zooxanthellae is symbiotic mutualism, in which coral reefs provide a place to live for algae while zooxanthellae provide nutrients resulting from the process of photosynthesis. However, when there is a change in temperature in seawater, the algae will leave their shelter for so long. When these tiny algae leave, the white outer part of the coral reef will be visible because polyps are colorless (transparent). This event is then referred to as coral bleaching.

As reported by National Geographic, until now coral reef bleaching has occurred around the globe, from Australia to Madagascar. From 2014 to 2017, the largest coral bleaching occurred, and has reached 70%. Although they are still able to survive without algae, coral reefs will become susceptible to disease. Especially if the temperature of the seawater increases, it is likely that coral reefs will die. Even if seawater temperatures return to normal and algae return to the coral reefs, it will take another 10 to 15 years for the coral reefs to fully recover.

Causes of Coral Bleaching

Dead Coral Reef Illustration
Dead Coral Reef Illustration. (Source: marineconservation.org.au)

The main cause of coral bleaching is due to changes in temperature, pollution, and overfishing of sea creatures. A change in seawater temperature, both above or below the normal temperature, can trigger a coral bleaching. Coral reefs can grow well in tropical seas at temperatures from 28 to 29 degrees Celsius.

When there is a temperature difference of 2 to 3 degrees Celsius above or below the normal temperature in one to two weeks, coral reefs will show signs of impending bleaching. When temperature changes occur up to one month, then the entire coral colony, soft coral, anemone, and zoanthid will turn white and eventually die in the sixth week.

The warm water mass in the ocean is also affected by the El Nino phenomenon. Meanwhile, the decrease in sea temperature is also affected by Indian Ocean Dipolemode. Coral bleaching in the western part of Sumatra, especially, is sometimes caused by a drop in subnormal temperatures of less than 26 degrees celsius.

Can Bleached Corals Recover?

Sightings Coral Bleaching Closely
Sightings Coral Bleaching Closely. (Source: gilisharkconservation.com)

Maybe these questions will arise in our minds after reading the description of coral bleaching. The restoration of coral reefs will depend on the type of coral reefs and the level of stress experienced by coral reefs due to changes in the temperature of the surrounding seawater.

Some coral reefs are very sensitive to temperature changes, such as coral reefs from the group Pociliporoid and Acroporoid. Meanwhile, there are also types of coral reefs that are strong enough to survive changes in seawater temperature, such as Porites and coral reefs polyp big. This type of coral reef will return to normal if the temperature increase is not more than six weeks to one month. However, if the increase in seawater temperature only occurs for two to three weeks, usually coral reefs can survive and will soon recover their original color.

In principle, actually coral reefs only experience stress when there’s change in water temperature, and once it returns to normal coral reefs will soon recover. A more extreme situation can occur, though, when coral reefs suffer from severe bleaching, followed by other factors that aggravate their surrounding environment. For example when coral bleaching takes place during the transitional season. In this condition, the seawater is very calm coupled with the maximum intensity of sunlight. Under these conditions, various growths will usually appear in filaments, turf algae, cyanobacteria, and coral disease. If this happens it will be very fatal.

Human Intervention on Coral Reef Restoration

Basically, coral reefs can heal themselves. However, you can also take various steps to restore bleached coral reefs, and prevent bleaching of healthy coral reefs.

Implementing sustainable consumption and production, in everyday life or when traveling, can be a solution. Even though they live far from the sea, Green Generation who grow crops can avoid the use of chemical fertilizers and pesticides so that chemical compounds do not enter waterways that will end up in the sea. Green Generation can also separate waste so that no garbage is scattered and ends up in the sea. At home, save water, in order to reduce the residual water that can pollute the sea.

When traveling to the beach, Green Generation can use environmentally friendly sunscreens, so that harmful chemical compounds do not dissolve in seawater when swimming. When diving or snorkeling, make sure the boat anchor does not touch the coral reefs. Also, make sure you don’t touch coral reefs, and no waste is dumped from ships into the sea. Lastly, of course, don’t throw trash on the beach or the sea, and join the activities volunteer cleaning the beach, like what EcoRanger friends did at Pulau Merah Beach, Banyuwangi.

In longer-term, halting global warming is the key to the prevention and recovery of coral bleaching. So, make sure also that Green Generation has taken steps to prevent global warming, such as switching to renewable energy, using public transportation or transportation without fossil fuels, and reading the carbon label on the products you consume.

Written by: Yohanna Christiani

References

http://coremap.or.id/berita/1172 accessed on 7 October 2021.

https://nationalgeographic.grid.id/read/

131623449/coral-bleaching-fenomena-hilangnya-warna-indah-terumbu-karang accessed on 7 October 2021.

https://reefresilience.org/id/stressors/

bleaching/ accessed on 7 October 2021.

https://www.kompas.com/sains/read/

2020/06/18/173000923/cegah-pemutihan-terumbu-karang-diberi-makan-bakteri-probiotik?page=all accessed on 7 October 2021.

https://www.instagram.com/p/

CUWZcP_h7Nz/ accessed on 7 October 2021.

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